UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-05099

Pioneer Money Market Trust

(Exact name of registrant as specified in charter)

60 State Street, Boston, MA 02109

(Address of principal executive offices) (ZIP code)

Terrence J. Cullen, Amundi Asset Management, Inc.,

60 State Street, Boston, MA 02109

(Name and address of agent for service)

Registrant’s telephone number, including area code:  (617) 742-7825

Date of fiscal year end:  December 31, 2021

Date of reporting period: January 1, 2021 through December 31, 2021

Form N-CSR is to be used by management investment companies to file reports with the Commission not later than 10 days after the transmission to stockholders of any report that is required to be transmitted to stockholders under Rule 30e-1 under the Investment Company Act of 1940 (17 CFR 270.30e-1).  The Commission may use the information provided on Form N-CSR in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-CSR, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-CSR unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609.  The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. ss. 3507.

Pioneer U.S. Government Money Market Fund

Annual Report | December 31, 2021

A: PMTXX R: PRXXX Y: PRYXX

visit us: www.amundi.com/us

Table of Contents
President’s Letter	2
Portfolio Management Discussion	4
Portfolio Summary	8
Prices and Distributions	9
Comparing Ongoing Fund Expenses	11
Schedule of Investments	13
Financial Statements	16
Notes to Financial Statements	23
Report of Independent Registered Public Accounting Firm	32
Additional Information	34
Approval of Renewal of Investment Management Agreement	35
Trustees, Officers and Service Providers	40

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 1

President’s LetterDear Shareholders,

For nearly two years now, investors have faced unprecedented challenges, as the COVID-19 pandemic has not only dominated the headlines since March 2020, but has also led to significant changes in government and central-bank policies, both in the US and abroad, and affected the everyday lives of each of us. As we move into 2022, the situation, while improved, has continued to evolve.

Widespread distribution of the COVID-19 vaccines approved for emergency use in late 2020 led to a general decline in virus-related hospitalizations in the US and had a positive effect on overall market sentiment during most of the 2021 calendar year. The passage of two additional fiscal stimulus packages by US lawmakers in December 2020 and January 2021 also helped drive a strong market rally. However, the emergence of highly infectious variants of the virus has caused occasional surges in cases and hospitalizations, especially outside of the US, but also in certain areas of this country. That development has contributed to a slowdown in the global economic recovery, as some foreign governments have reinstated strict virus-containment measures that had been relaxed after the rollout of the vaccines.

In the US, while performance of most asset classes, especially equities, was positive for the full 2021 calendar year, volatility was and has remained high. Concerns over global supply chain issues, rising inflation, “hawkish” signals concerning less-accommodative future monetary policies from the Federal Reserve System (Fed), and partisan debates in Washington, DC over future spending and tax policies, are among the many factors that have led to greater uncertainty and an increase in market volatility.

Despite those issues, and some of the recent difficulties that have affected the economy and the markets, we believe the distribution of the COVID-19 vaccines has provided a potential light at the end of the pandemic tunnel. With that said, the long-term impact on the global economy from COVID-19, while currently unknown, is likely to be considerable, as it is clear that several industries have already felt greater effects than others, and could continue to struggle for quite some time.

After leaving our offices in March of 2020 due to COVID-19, we have re-opened our US locations, but are maintaining all the necessary precautions, which at times may have us working more remotely than in person in order to ensure a safe working environment as new variants of the COVID-19 virus continue to arise and spread. I am proud of the careful

2 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

planning that has taken place. Throughout the pandemic, our business has continued to operate without any disruption, and we all look forward to regaining a bit of normalcy after so many months of remote working.

Since 1928, Amundi US’s investment process has been built on a foundation of fundamental research and active management, principles which have guided our investment decisions for more than 90 years. We believe active management – that is, making active investment decisions – can help mitigate the risks during periods of market volatility.

At Amundi US, active management begins with our own fundamental, bottom-up research process. Our team of dedicated research analysts and portfolio managers analyzes each security under consideration, communicating directly with the management teams of the companies issuing the securities and working together to identify those securities that best meet our investment criteria for our family of funds. Our risk management approach begins with each and every security, as we strive to carefully understand the potential opportunity, while considering any and all risk factors.

Today, as investors, we have many options. It is our view that active management can serve shareholders well, not only when markets are thriving, but also during periods of market stress.

As you consider your long-term investment goals, we encourage you to work with your financial professional to develop an investment plan that paves the way for you to pursue both your short-term and long-term goals.

We greatly appreciate the trust you have placed in us and look forward to continuing to serve you in the future.

Sincerely,

Lisa M. Jones
Head of the Americas, President and CEO of US
Amundi Asset Management US, Inc.
February 2022

Any information in this shareowner report regarding market or economic trends or the factors influencing the Fund’s historical or future performance are statements of opinion as of the date of this report. Past performance is no guarantee of future results.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 3

Portfolio Management Discussion | 12/31/21

In the following discussion, Portfolio Manager Gregory Palmer reviews the factors that affected the performance of Pioneer US Government Money Market Fund during the 12-month period. Mr. Palmer, a vice president and a portfolio manager at Amundi Asset Management US, Inc. (Amundi US), is responsible for the daily management of the Fund, along with Timothy Rowe*, Managing Director, Director of Multi-Sector Fixed Income, and a portfolio manager at Amundi US.

Q How did the Fund perform during the 12-month period ended December 31, 2021?

A Pioneer US Government Money Market Fund’s Class A shares returned 0.02% at net asset value during the 12-month period ended December 31, 2021.

Q How would you describe the environment for money market investing during the12-month period ended December 31, 2021?

A The first quarter of 2021 saw strong returns in the equity markets, notably higher longer-term US Treasury yields, and rising inflation expectations, driven by investor optimism regarding the global economic growth outlook. Contributing to the optimistic view was the Democrats’ early-January takeover of both houses of Congress, which led to passage of a new $1.9 trillion US fiscal stimulus package and, later, a proposed $3 billion-plus infrastructure bill. In addition, the continued rollout and distribution of COVID-19 vaccines in the US as well as a general decline in new virus cases, coupled with the ongoing reopening of the economy, boosted market sentiment in the first few months of 2021.

Moving into the second quarter of 2021, the continued highly-dovish posture on monetary policy from the US Federal Reserve (Fed) lent further support to the markets for riskier assets such as stocks and corporate bonds, as the US central bank expressed its intention to remain “on the sidelines” with regard to major policy changes until at least 2023. The Fed based its projection on the view that near-term increases in inflation above the usual 2% target were likely to be transitory, and not structural. The Fed also messaged that it would look at average inflation over time, rather than feeling compelled to raise rates based on an isolated uptick in prices.

* Mr. Rowe became a portfolio manager on the Fund effective September 29, 2021.

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However, the “reflation trade” wobbled during June 2021 as investors navigated through growing apprehension over the emergence and spread of COVID-19 variants and a somewhat “hawkish” Fed Open Market Committee (FOMC) meeting that month. The updated Fed “dot plot” displaying the forecasts for the federal funds rate pointed to a median year-end 2023 federal funds target rate of 0.625%, or 50 basis points (bps) higher than the March forecast. (The Fed’s “dot” plot/projection is a quarterly chart summarizing the outlook for the federal funds rate for each FOMC meeting participant. A basis point is equal to 1/100th of a percentage point.) The market’s reaction suggested investors’ doubts regarding the Fed’s long-term commitment to its new average-inflation targeting framework.

The second half of the Fund’s fiscal year saw persistently high and accelerating inflation readouts. With unemployment levels approaching their historically low pre-pandemic levels, the Fed signaled that it was prepared to begin reducing (“tapering”) its monthly purchases of Treasuries and mortgage-backed securities, which had been deployed in the spring of 2020 (after the onset of the pandemic) to help keep longer-term borrowing costs low. In November, the Fed officially launched the tapering of its bond purchases. With November inflation data surprising to the upside, the Fed announced in December that it would double the pace of the tapering, while the updated December FOMC dot plot indicated the likelihood of three increases in the federal funds rate’s target range in 2022, with more increases potentially on tap for 2023.

Short-term Treasury yields drifted higher over the fourth quarter of 2021, as markets began to factor in an earlier (than previously anticipated) “lift off” in the federal funds rate. Yields for six-month and one-year Treasury bills ended 2021 at 0.19%, and 0.39%, respectively, compared with 0.09% (six month) and 0.10% (one year) at the end of 2020, while one-month yields remained relatively flat.

Q How did you manage the Fund’s portfolio in that environment during the 12-month period ended December 31, 2021?

A We have continued to pursue a very conservative investment policy, and have remained focused on our primary objective in managing the Fund: protecting shareholders’ capital, rather than taking on undue risk in search of slightly higher total returns.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 5

Given the Fund’s objective, and with the front end of the money market yield curve remaining very flat during the 12-month period, we felt there was little incentive to extend the portfolio’s duration. Thus, we generally kept the average maturity of the securities held in the Fund’s portfolio relatively low. (Duration is a measure of the sensitivity of the price, or the value of principal, of a fixed-income investment to a change in interest rates, expressed as a number of years.)

The weighted average maturity in the portfolio gradually decreased over the course of the 12-month period, with an average maturity of 20 to 22 days during the first six months of the period, and decreasing to an average of 10 days towards the end of the Fund’s fiscal year, as the timetable for anticipated Fed rate hikes accelerated to within a three-to-four month window (with an initial rate increase possible as early as March of 2022).

We maintained a significant allocation in the portfolio to overnight repurchase agreements that were fully collateralized by Treasury and agency securities, and that provided yields only marginally lower than those of one-year Treasury bills, given the flat curve. We also maintained an allocation in the Fund to US Treasury floating-rate notes with coupons that reset daily (based on a spread above three-month bills), which have offered incremental income with little interest-rate risk. Finally, the Fund had exposures to US agency floating-rate notes with coupons based on the benchmark secured overnight financing rate, and to short-term agency fixed-coupon notes.

Q What is your investment outlook?

A With inflation and labor-market data hitting the target levels the Fed had set near the beginning of the pandemic, the central bank began tapering its asset purchases at the end of 2021 and, as noted earlier, has signaled that it anticipates raising the federal funds rate’s target range in early 2022. Entering the Fund’s new fiscal year, federal funds futures were pricing in three rate hikes in the coming 12 months. As a result, we have continued to be wary of extending the portfolio’s duration.

The Fund remains positioned with significant allocations to overnight repurchase agreements and floating-rate notes. Additionally, if we are able to identify relatively inexpensive fixed-coupon agency debt, we may look to add more of those securities to the portfolio. Overall, we anticipate continuing to maintain a conservative positioning for the Fund, one that focuses on stability of principal, first and foremost.

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Please refer to the Schedule of Investments on pages 13–15 for a full listing of Fund securities.

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

All investments are subject to risk, including the possible loss of principal. In the past several years, financial markets have experienced increased volatility and heightened uncertainty. The market prices of securities may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, recessions, inflation, changes in interest or currency rates, lack of liquidity in the bond markets, the spread of infectious illness or other public health issues or adverse investor sentiment. These conditions may continue, recur, worsen or spread.

The securities issued by U.S. Government-sponsored entities (e.g., FNMA, Freddie Mac) are neither guaranteed nor issued by the U.S. Government.

At times, the Fund’s investments may represent industries or industry sectors that are interrelated or have common risks, making the Fund more susceptible to any economic, political, or regulatory developments or other risks affecting those industries and sectors.

These risks may increase share price volatility.

Before investing, consider the product’s investment objectives, risks, charges and expenses. Contact your financial professional or Amundi Asset Management US, Inc., for a prospectus or summary prospectus containing this information. Read it carefully.

Any information in this shareholder report regarding market or economic trends or the factors influencing the Fund’s historical or future performance are statements of opinion as of the date of this report. Past performance is no guarantee of future results.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 7

Portfolio Summary | 12/31/21

10 Largest Holdings
(As a percentage of total investments)*
1.	U.S. Treasury Floating Rate Notes, 0.274% (3 Month U.S. Treasury
	Bill Money Market Yield + 15 bps), 1/31/22	10.86%
2.	U.S. Treasury Floating Rate Notes, 0.234% (3 Month U.S. Treasury
	Bill Market Yield + 11 bps), 4/30/22	8.47
3.	U.S. Treasury Floating Rate Notes, 0.175% (3 Month U.S. Treasury
	Bill Money Market Yield + 6 bps), 10/31/22	7.38
4.	U.S. Treasury Bills, 1/11/22	6.42
5.	U.S. Treasury Bills, 1/13/22	5.54
6.	Federal National Mortgage Association, 0.28% (SOFRRATE + 23 bps), 5/6/22	3.69
7.	U.S. Treasury Floating Rate Notes, 0.175% (3 Month U.S. Treasury
	Bill Market Yield + 6 bps), 7/31/22	3.69
8.	Federal National Mortgage Association, 2.625%, 1/11/22	3.08
9.	Federal Home Loan Mortgage Corp., 2.375%, 1/13/22	2.98
10.	U.S. Treasury Bills, 1/6/22	2.58

* Excludes derivative contracts except for options purchased. The Fund is actively managed, and current holdings may be different. The holdings listed should not be considered recommendations to buy or sell any securities.

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Prices and Distributions | 12/31/21

Net Asset Value per Share

Class	12/31/21	12/31/20
A	$1.00	$1.00
R	$1.00	$1.00
Y	$1.00	$1.00

Distributions per Share: 1/1/21 – 12/31/21
	Net Investment	Short-Term	Long-Term
Class	Income	Capital Gains	Capital Gains
A	$0.0002	$ —	$ —
R	$0.0002	$ —	$ —
Y	$0.0002	$ —	$ —

Yields
Class	7-Day Annualized*	7-Day Effective**
A	0.01%	0.01%
R	0.01%	0.01%
Y	0.01%	0.01%

* The 7-day annualized net yield describes the annualized income earned over a 7-day period.

** The 7-day effective yield describes the amount one is expected to earn over a 1-year period assuming that dividends are reinvested at the average rate of the last 7-days.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 9

Expense Ratio (Per prospectus dated May 1, 2021)

Class	Gross
A	0.79%
R	1.08%
Y	0.53%

Call 1-800-225-6292 or visit www.amundi.com/us for the most recent month-end performance results. Current performance may be lower or higher than the performance data quoted.

The performance data quoted represents past performance, which is no guarantee of future results.

Investment return and principal value will fluctuate, and shares, when redeemed, may be worth more or less than their original cost.

Amundi US has agreed to limit the Fund’s expenses for any class of shares or waive a portion of its management fee in an effort to maintain a net asset value of $1.00 per share. From time to time, Amundi US and its affiliates may limit the expenses of one or more classes for the purpose of avoiding a negative yield or increasing its yield during the period of the limitation. These expense limitation policies are voluntary and temporary and may be revised or terminated by Amundi US at any time without notice.

Please refer to the financial highlights for a more current expense ratio.

Performance does not reflect the deduction of taxes that a shareowner would pay on Fund distributions or the redemption of Fund shares.

10 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Comparing Ongoing Fund Expenses

As a shareowner in the Fund, you incur two types of costs:

(1) ongoing costs, including management fees, distribution and/or service (12b-1) fees, and other Fund expenses; and

(2) transaction costs, including sales charges (loads) on purchase payments.

This example is intended to help you understand your ongoing expenses (in dollars) of investing in the Fund and to compare these costs with the ongoing costs of investing in other mutual funds. The example is based on an investment of $1,000 at the beginning of the Fund’s latest six-month period and held throughout the six months.

Using the Tables

Actual Expenses

The first table below provides information about actual account values and actual expenses.You may use the information in this table, together with the amount you invested, to estimate the expenses that you paid over the period as follows:

(1) Divide your account value by $1,000

Example: an $8,600 account value ÷ $1,000 = 8.6

(2) Multiply the result in (1) above by the corresponding share class’s number in the third row under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Expenses Paid on a $1,000 Investment in Pioneer U.S. Government Money Market Fund

Based on actual returns from July 1, 2021 through December 31, 2021.

Share Class	A	R	Y
Beginning Account	$1,000.00	$1,000.00	$1,000.00
Value on 7/1/21
Ending Account	$1,000.20	$1,000.20	$1,000.20
Value on 12/31/21
Expenses Paid	$0.20	$0.30	$0.25
During Period*

* Expenses are equal to the Fund’s annualized expense ratio of 0.04%, 0.06%, and 0.05% for Class A, Class R, and Class Y shares, respectively, multiplied by the average account value over the period, multiplied by 184/365 (to reflect the one-half year period).

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 11

Hypothetical Example for Comparison Purposes

The table below provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the Fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period.

You may use this information to compare the ongoing costs of investing in the Fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the tables are meant to highlight your ongoing costs only and do not reflect any transaction costs, such as sales charges (loads) that are charged at the time of the transaction. Therefore, the table below is useful in comparing ongoing costs only and will not help you determine the relative total costs of owning different funds. In addition, if these transaction costs were included, your costs would have been higher.

Expenses Paid on a $1,000 Investment in Pioneer U.S. Government Money Market Fund

Based on a hypothetical 5% per year return before expenses, reflecting the period from July 1, 2021 through December 31, 2021.

Share Class	A	R	Y
Beginning Account	$1,000.00	$1,000.00	$1,000.00
Value on 7/1/21
Ending Account	$1,025.00	$1,024.90	$1,024.95
Value on 12/31/21
Expenses Paid	$0.20	$0.31	$0.26
During Period*

* Expenses are equal to the Fund’s annualized expense ratio of 0.04%, 0.06%, and 0.05% for Class A, Class R, and Class Y shares, respectively, multiplied by the average account value over the period, multiplied by 184/365 (to reflect the one-half year period).

12 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Schedule of Investments | 12/31/21

Principal
Amount ($)		Value
	UNAFFILIATED ISSUERS — 99.9%
	U.S. GOVERNMENT AND AGENCY OBLIGATIONS —
	65.3% of Net Assets
2,300,000(a)	Federal Farm Credit Banks Funding Corp., 0.095%,
	(SOFRRATE + 5 bps), 8/25/22	$ 2,300,532
1,500,000(a)	Federal Home Loan Banks, 0.110%, (SOFRRATE +
	6 bps), 12/8/22	1,500,281
1,020,000	Federal Home Loan Banks, 2.125%, 6/10/22	1,028,838
995,000	Federal Home Loan Banks, 2.250%, 3/11/22	999,155
2,270,000	Federal Home Loan Banks, 2.500%, 3/11/22	2,280,598
8,057,000	Federal Home Loan Mortgage Corp., 2.375%, 1/13/22	8,063,055
5,000,000(a)	Federal National Mortgage Association, 0.170%,
	(SOFRRATE + 12 bps), 7/29/22	5,003,051
6,000,000(a)	Federal National Mortgage Association, 0.270%,
	(SOFRRATE + 22 bps), 3/16/22	6,002,451
10,000,000(a)	Federal National Mortgage Association, 0.280%,
	(SOFRRATE + 23 bps), 5/6/22	10,007,668
200,000(a)	Federal National Mortgage Association, 0.410%,
	(SOFRRATE + 36 bps), 1/20/22	200,036
3,119,000	Federal National Mortgage Association, 1.875%, 4/5/22	3,133,397
5,385,000	Federal National Mortgage Association, 2.000%, 1/5/22	5,386,136
1,156,000	Federal National Mortgage Association, 2.250%, 4/12/22	1,162,971
8,330,000	Federal National Mortgage Association, 2.625%, 1/11/22	8,335,815
7,000,000(b)	U.S. Treasury Bills, 1/6/22	6,999,956
17,400,000(b)	U.S. Treasury Bills, 1/11/22	17,399,868
15,000,000(b)	U.S. Treasury Bills, 1/13/22	14,999,738
10,000,000(a)	U.S. Treasury Floating Rate Notes, 0.175%, (3 Month U.S.
	Treasury Bill Market Yield + 6 bps), 7/31/22	10,001,824
20,000,000(a)	U.S. Treasury Floating Rate Notes, 0.175%, (3 Month U.S.
	Treasury Bill Money Market Yield +
	6 bps), 10/31/22	20,006,199
22,950,000(a)	U.S. Treasury Floating Rate Notes, 0.234%, (3 Month U.S.
	Treasury Bill Market Yield + 11 bps), 4/30/22	22,956,695
29,415,000(a)	U.S. Treasury Floating Rate Notes, 0.274%, (3 Month U.S.
	Treasury Bill Money Market Yield + 15 bps), 1/31/22	29,418,014
	TOTAL U.S. GOVERNMENT AND AGENCY OBLIGATIONS
	(Cost $177,186,278)	$177,186,278

The accompanying notes are an integral part of these financial statements.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 13

Schedule of Investments | 12/31/21 (continued)

Principal
Amount ($)		Value
	SHORT TERM INVESTMENTS — 34.6% of
	Net Assets
	Repurchase Agreements — 34.6%
24,580,000	$24,580,000 Scotia Capital Inc., 0.05%, dated 12/31/21
	plus accrued interest on 1/3/22 collateralized
	by the following:
	$628,479 Federal Home Loan Mortgage Corporation,
	2.0%-4.5%, 3/1/31-4/1/51,
	$80,011 Federal National Mortgage Association,
	3.5%-4.5%,7/1/33-3/1/49,
	$24,363,227 U.S. Treasury Bills, 1/20/22-4/7/22	$ 24,580,000
24,580,000	$24,580,000 RBC Dominion Securities Inc., 0.05%, dated
	12/31/21 plus accrued interest on 1/3/22
	collateralized by the following:
	$18,322,168 Federal Home Loan Mortgage Corporation,
	2.0%-3.0%, 4/1/51-12/1/51,
	$4,437,487 Federal National Mortgage Association,
	3.0%, 12/1/50,
	$2,312,050 Government National Mortgage Association,
	3.0%-4.0%, 1/2/49-12/20/51	24,580,000
24,580,000	$24,580,000 Toronto-Dominion Bank, 0.05%, dated
	12/31/21 plus accrued interest on 1/3/22 collateralized by
	$25,071,721 U.S. Treasury Notes, 0.625%, 8/15/30	24,580,000
20,000,000	$20,000,000 Bank of America, 0.05%, dated 12/31/21 plus
	accrued interest on 1/3/22 collateralized by
	$20,400,084 U.S. Treasury Notes, 1.75%, 12/31/24	20,000,000
		$ 93,740,000
	TOTAL SHORT TERM INVESTMENTS
	(Cost $93,740,000)	$ 93,740,000
	TOTAL INVESTMENTS IN UNAFFILIATED ISSUERS — 99.9%
	(Cost $270,926,278)	$270,926,278
	OTHER ASSETS AND LIABILITIES — 0.1%	$ 200,726
	NET ASSETS — 100.0%	$271,127,004

bps	Basis Points
SOFRRATE	Secured Overnight Financing Rate
(a)	Floating rate note. Coupon rate, reference index and spread shown at December 31, 2021.
(b)	Security issued with a zero coupon. Income is recognized through accretion of discount.

The Fund is permitted to engage in purchase and sale transactions (“cross trades”) with certain funds and accounts for which Amundi Asset Management US, Inc. (the “Adviser”) serves as the Fund’s investment adviser, as set forth in Rule 17a-7 under the Investment Company Act of 1940, pursuant to procedures adopted by the Board of Trustees. Under these procedures, cross trades are effected at current market prices. During the year ended December 31, 2021, the Fund did not engage in any cross trade activity.

The accompanying notes are an integral part of these financial statements.

14 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

At December 31, 2021, the net unrealized depreciation on investments based on cost for federal tax purposes of $270,926,496 was as follows:

Aggregate gross unrealized appreciation for all investments in which
there is an excess of value over tax cost	$ —
Aggregate gross unrealized depreciation for all investments in which
there is an excess of tax cost over value	(218)
Net unrealized depreciation	$(218)

Various inputs are used in determining the value of the Fund’s investments. These inputs are summarized in the three broad levels below.

Level 1 – unadjusted quoted prices in active markets for identical securities.

Level 2 – other significant observable inputs (including quoted prices for similar securities, interest rates, prepayment speeds, credit risks, etc.). See Notes to Financial Statements —Note  1A.

Level 3 – significant unobservable inputs (including the Fund’s own assumptions in determining fair value of investments). See Notes to Financial Statements — Note 1A.

The following is a summary of the inputs used as of December 31, 2021, in valuing the Fund’s investments:

	Level 1	Level 2	Level 3	Total
U.S. Government and
Agency Obligations	$ —	$177,186,278	$ —	$177,186,278
Repurchase Agreements	—	93,740,000	—	93,740,000
Total Investments in Securities	$ —	$270,926,278	$ —	$270,926,278

During the year ended December 31, 2021, there were no transfers in or out of Level 3.

The accompanying notes are an integral part of these financial statements.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 15

Statement of Assets and Liabilities | 12/31/21

ASSETS:
Investments in unaffiliated issuers, at value (cost $270,926,278)	$270,926,278
Cash	2,421,631
Receivables —
Fund shares sold	305,214
Interest	321,418
Due from the Adviser	7,241
Other assets	25,080
Total assets	$274,006,862
LIABILITIES:
Payables —
Investment securities purchased	$ 1,770,378
Fund shares repurchased	843,532
Distributions	425
Trustees’ fees	1,037
Professional fees	52,222
Shareowner communications expense	57,790
Due to affiliates
Management fees	7,752
Other due to affiliates	19,233
Accrued expenses	127,489
Total liabilities	$ 2,879,858
NET ASSETS:
Paid-in capital	$271,069,844
Distributable earnings	57,160
Net assets	$271,127,004
NET ASSET VALUE PER SHARE:
No par value (unlimited number of shares authorized)
Class A (based on $215,527,794/215,612,398 shares)	$ 1.00
Class R (based on $1,584,509/1,584,500 shares)	$ 1.00
Class Y (based on $54,014,701/54,024,940 shares)	$ 1.00

The accompanying notes are an integral part of these financial statements.

16 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Statement of Operations

FOR THE YEAR ENDED 12/31/21

INVESTMENT INCOME:
Interest from unaffiliated issuers	$ 199,472
Total Investment Income		$ 199,472
EXPENSES:
Management fees	$1,006,010
Administrative expenses	193,827
Transfer agent fees
Class A	203,253
Class R	1,076
Class Y	1,176
Distribution fees
Class A	349,420
Class R	7,995
Shareowner communications expense	109,086
Custodian fees	29,609
Registration fees	80,300
Professional fees	60,142
Printing expense	53,775
Trustees’ fees	10,526
Insurance expense	671
Miscellaneous	19,264
Total expenses		$ 2,126,130
Less fees waived and expenses reimbursed
by the Adviser and Distributor		(2,006,682)
Net expenses		$ 119,448
Net investment income		$ 80,024
REALIZED AND UNREALIZED GAIN (LOSS) ON INVESTMENTS:
Net realized gain (loss) on:
Investments in unaffiliated issuers		1,969
Net increase in net assets resulting from operations		$ 81,993

The accompanying notes are an integral part of these financial statements.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 17

Statements of Changes in Net Assets

	Year	Year
	Ended	Ended
	12/31/21	12/31/20
FROM OPERATIONS:
Net investment income (loss)	$ 80,024	$ 489,485
Net realized gain (loss) on investments	1,969	19,614
Net increase in net assets resulting from operations	$ 81,993	$ 509,099
DISTRIBUTIONS TO SHAREOWNERS:
Class A ($0.0002 and $0.0020 per share, respectively)	$ (44,571)	$ (395,370)
Class R ($0.0002 and $0.0012 per share, respectively)	(314)	(1,200)
Class Y ($0.0002 and $0.0022 per share, respectively)	(10,720)	(94,677)
Total distributions to shareowners	$ (55,605)	$ (491,247)
FROM FUND SHARE TRANSACTIONS:
Net proceeds from sales of shares	$ 128,388,791	$ 257,625,793
Reinvestment of distributions	45,462	397,362
Cost of shares repurchased	(164,915,034)	(190,719,800)
Net increase (decrease) in net assets resulting
from Fund share transactions	$ (36,480,781)	$ 67,303,355
Net increase (decease) in net assets	$ (36,454,393)	$ 67,321,207
NET ASSETS:
Beginning of year	$ 307,581,397	$ 240,260,190
End of year	$ 271,127,004	$ 307,581,397

The accompanying notes are an integral part of these financial statements.

18 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

	Year	Year	Year	Year
	Ended	Ended	Ended	Ended
	12/31/21	12/31/21	12/31/20	12/31/20
	Shares	Amount	Shares	Amount
Class A
Shares sold	100,527,332	$ 100,527,332	232,828,184	$ 232,840,618
Reinvestment of distributions	44,571	44,571	395,370	395,370
Less shares repurchased	(142,285,241)	(142,283,571)	(173,074,246)	(173,074,247)
Net increase/(decrease)	(41,713,338)	$ (41,711,668)	60,149,308	$ 60,161,741
Class R
Shares sold	773,794	$ 773,794	1,666,294	$ 1,666,381
Reinvestment of distributions	314	314	1,200	1,200
Less shares repurchased	(1,014,624)	(1,014,880)	(727,340)	(727,340)
Net increase/(decrease)	(240,516)	$ (240,772)	940,154	$ 940,241
Class Y
Shares sold	27,087,665	$ 27,087,665	23,116,448	$ 23,118,794
Reinvestment of distributions	577	577	792	792
Less shares repurchased	(21,616,446)	(21,616,583)	(16,918,213)	(16,918,213)
Net increase	5,471,796	$ 5,471,659	6,199,027	$ 6,201,373

The accompanying notes are an integral part of these financial statements.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 19

Financial Highlights

	Year		Year		Year		Year		Year
	Ended		Ended		Ended		Ended		Ended
	12/31/21		12/31/20		12/31/19		12/31/18		12/31/17
Class A
Net asset value, beginning of period	$ 1.00		$ 1.00		$ 1.00		$ 1.00		$ 1.00
Increase (decrease) from investment operations:
Net investment income (loss) (a)	$ 0.000(b)		$ 0.002		$ 0.015		$ 0.012		$ 0.003
Net realized and unrealized gain (loss) on investments (b)	0.000		0.000		0.000		0.000		0.000
Net increase (decrease) from investment operations	$ 0.000(b)		$ 0.002		$ 0.015		$ 0.012		$ 0.003
Distributions to shareowners:
Net investment income	$ (0.000)(b)		$ (0.002)(c)		$ (0.015)(c)		$ (0.012)(c)		$ (0.003)
Net increase (decrease) in net asset value	$ 0.00		$ 0.00		$ 0.00		$ 0.00		$ 0.00
Net asset value, end of period	$ 1.00		$ 1.00		$ 1.00		$ 1.00		$ 1.00
Total return (d)		0.02%		0.20%		1.50%		1.21%		0.27%
Ratio of net expenses to average net assets		0.04%		0.25%		0.69%		0.66%		0.62%
Ratio of net investment income (loss) to average net assets		0.03%		0.16%		1.50%		1.20%		0.26%
Net assets, end of period (in thousands)	$215,528		$257,214		$197,032		$210,290		$217,256
Ratios with no waiver of fees and assumption of expenses by
the Adviser and no reduction for fees paid indirectly:
Total expenses to average net assets		0.79%		0.79%		0.84%		0.81%		0.80%
Net investment income (loss) to average net assets	(0.72)%		(0.38)%			1.35%		1.05%		0.08%

(a) The per-share data presented above is based on the average shares outstanding for the period presented.

(b) Amount rounds to less than $0.001 or $(0.001) per share.

(c) The amount of distributions made to shareowners during the period were in excess of the net investment income earned by the Fund during the period. A portion of the accumulated net investment income was distributed to shareowners during the period.

(d) Assumes initial investment at net asset value at the beginning of each period, reinvestment of all distributions, the complete redemption of the investment at net asset value at the end of each period and no sales charges. Total return would be reduced if sales charges were taken into account.

The accompanying notes are an integral part of these financial statements.

20 Pioneer U. S. Government Money Market Fund | Annual Report | 12/31/21

	Year	Year	Year	Year
	Ended	Ended	Ended	Ended	8/1/17* to
	12/31/21	12/31/20	12/31/19	12/31/18	12/31/17
Class R
Net asset value, beginning of period	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00
Increase (decrease) from investment operations:
Net investment income (loss) (a)	$ 0.000(b)	$ 0.001	$ 0.010	$ 0.009	$ 0.000(b)
Net realized and unrealized gain (loss) on investments	0.000(b)	0.000(b)	0.001	(0.001)	0.000(b)
Net increase (decrease) from investment operations	$ 0.000(b)	$ 0.001	$ 0.011	$ 0.008	$ 0.000(b)
Distributions to shareowners:
Net investment income	$(0.000)(b)	$(0.001)(c)	$(0.011)(c)	$(0.008)(c)	$ 0.000(b)
Net increase (decrease) in net asset value	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net asset value, end of period	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00
Total return (d)	0.02%	0.12%	1.08%	0.78%	0.03%(e)
Ratio of net expenses to average net assets	0.06%	0.30%	1.12%	1.08%	1.02%(f)
Ratio of net investment income (loss) to average net assets	0.01%	0.09%	1.03%	0.85%	0.10%(f)
Net assets, end of period (in thousands)	$ 1,585	$ 1,825	$ 885	$ 553	$ 151
Ratios with no waiver of fees and assumption of expenses by
the Adviser and no reduction for fees paid indirectly:
Total expenses to average net assets	1.11%	1.08%	1.12%	1.08%	1.03%(f)
Net investment income (loss) to average net assets	(1.04)%	(0.69)%	1.03%	0.85%	0.09%(f)

* Class R shares commenced operations on August 1, 2017.

(a) The per-share data presented above is based on the average shares outstanding for the period presented.

(b) Amount rounds to less than $0.001 or $(0.001) per share.

(c) The amount of distributions made to shareowners during the period were in excess of the net investment income earned by the Fund during the period. A portion of the accumulated net investment income was distributed to shareowners during the period.

(d) Assumes initial investment at net asset value at the beginning of each period, reinvestment of all distributions and the complete redemption of the investment at net asset value at the end of each period.

(e) Not annualized.

(f) Annualized.

The accompanying notes are an integral part of these financial statements.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 21

Financial Highlights (continued)

	Year	Year	Year	Year	Year
	Ended	Ended	Ended	Ended	Ended
	12/31/21	12/31/20	12/31/19	12/31/18	12/31/17
Class Y
Net asset value, beginning of period	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00
Increase (decrease) from investment operations:
Net investment income (loss) (a)	$ 0.000(b)	$ 0.002	$ 0.017	$ 0.013	$ 0.004
Net realized and unrealized gain (loss) on investments	0.000(b)	0.000(b)	0.000(b)	0.001	0.000(b)
Net increase (decrease) from investment operations	$ 0.000(b)	$ 0.002	$ 0.017	$ 0.014	$ 0.004
Distributions to shareowners:
Net investment income	$ (0.000)(b)	$ (0.002)(c)	$ (0.017)(c)	$ (0.014)(c)	$ (0.004)
Net increase (decrease) in net asset value	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Net asset value, end of period	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00
Total return (d)	0.02%	0.22%	1.67%	1.34%	0.37%
Ratio of net expenses to average net assets	0.05%	0.24%	0.52%	0.54%	0.51%
Ratio of net investment income (loss) to average net assets	0.02%	0.19%	1.66%	1.30%	0.36%
Net assets, end of period (in thousands)	$54,015	$48,542	$42,343	$37,356	$49,178
Ratios with no waiver of fees and assumption of expenses by
the Adviser and no reduction for fees paid indirectly:
Total expenses to average net assets	0.51%	0.53%	0.52%	0.54%	0.51%
Net investment income (loss) to average net assets	(0.44)%	(0.10)%	1.66%	1.30%	0.36%

(a) The per-share data presented above is based on the average shares outstanding for the period presented.

(b) Amount rounds to less than $0.001 or $(0.001) per share.

(c) The amount of distributions made to shareowners during the period were in excess of the net investment income earned by the Fund during the period. A portion of the accumulated net investment income was distributed to shareowners during the period.

(d) Assumes initial investment at net asset value at the beginning of each period, reinvestment of all distributions and the complete redemption of the investment at net asset value at the end of each period.

The accompanying notes are an integral part of these financial statements.

22 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Notes to Financial Statements | 12/31/21

1. Organization and Significant Accounting Policies

Pioneer U.S. Government Money Market Fund (the “Fund”) is a series of Pioneer Money Market Trust (the “Trust”), a Delaware statutory trust. The Fund is registered under the Investment Company Act of 1940 as a diversified, open-end management investment company. The investment objective of the Fund is to provide high current income, preservation of capital, and liquidity through investments in high-quality short-term securities.

The Fund offers three classes of shares designated as Class A, Class R and Class Y shares. Class R shares commenced operations on August 1, 2017. Each class of shares represents an interest in the same portfolio of investments of the Fund and has identical rights (based on relative net asset values) to assets and liquidation proceeds. Share classes can bear different rates of class-specific fees and expenses such as transfer agent and distribution fees. Differences in class-specific fees and expenses will result in differences in net investment income and, therefore, the payment of different dividends from net investment income earned by each class. The Amended and Restated Declaration of Trust of the Trust gives the Board of Trustees the flexibility to specify either per-share voting or dollar-weighted voting when submitting matters for shareowner approval. Under per-share voting, each share of a class of the Fund is entitled to one vote. Under dollar-weighted voting, a shareowner’s voting power is determined not by the number of shares owned, but by the dollar value of the shares on the record date. Each share class has exclusive voting rights with respect to matters affecting only that class, including with respect to the distribution plan for that class. There is no distribution plan for Class Y shares.

Amundi Asset Management US, Inc., an indirect, wholly owned subsidiary of Amundi and Amundi’s wholly owned subsidiary, Amundi USA, Inc., serves as the Fund’s investment adviser (the “Adviser”). Amundi Distributor US, Inc., an affiliate of the Adviser serves as the Fund’s distributor (the “Distributor”).

In March 2020, FASB issued an Accounting Standard Update, ASU 2020-04, Reference Rate Reform (Topic 848) — Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”), which provides optional, temporary relief with respect to the financial reporting of contracts subject to certain types of modifications due to the planned discontinuation of the London Interbank Offered Rate (“LIBOR”) and other LIBOR-based reference rates at the end of 2021. The temporary relief

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 23

provided by ASU 2020-04 is effective for certain reference rate-related contract modifications that occur during the period from March 12, 2020 through December 31, 2022. Management is evaluating the impact of ASU 2020-04 on the Fund’s investments, derivatives, debt and other contracts, if applicable, that will undergo reference rate-related modifications as a result of the reference rate reform.

The Fund is an investment company and follows investment company accounting and reporting guidance under U.S. Generally Accepted Accounting Principles (“U.S. GAAP”). U.S. GAAP requires the management of the Fund to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of income, expenses and gain or loss on investments during the reporting period. Actual results could differ from those estimates.

The following is a summary of significant accounting policies followed by the Fund in the preparation of its financial statements:

A. Security Valuation

The net asset value of the Fund is computed twice daily, on each day the New York Stock Exchange (“NYSE”) is open, at 1:00 p.m. Eastern time and as of the close of regular trading on the NYSE (normally 4:00 p.m. Eastern time).

The Fund generally values its securities using the amortized cost method, which approximates fair market value, in accordance with Rule 2a-7 under the 1940 Act. This valuation method assumes a steady rate of amortization of any premium or discount from the date of purchase until the maturity of each security. This valuation method is designed to permit a money market fund to maintain a constant net asset value of $1.00 per share, but there is no guarantee that it will do so.

Shares of open-end registered investment companies (including money market mutual funds) are valued at such funds’ net asset value.

Repurchase agreements are valued at par. Cash may include overnight time deposits at approved financial institutions.

B. Investment Income and Transactions

Investments purchased at a discount or premium are valued by amortizing the difference between the original purchase price and maturity value of the issue over the period to maturity.

Interest income, including interest on income-bearing cash accounts, is recorded on the accrual basis.

24 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Security transactions are recorded as of trade date. Gains and losses on sales of investments are calculated on the identified cost method for both financial reporting and federal income tax purposes.

C. Federal Income Taxes

It is the Fund’s policy to comply with the requirements of the Internal Revenue Code applicable to regulated investment companies and to distribute all of its net taxable income and net realized capital gains, if any, to its shareowners. Therefore, no provision for federal income taxes is required. As of December 31, 2021, the Fund did not accrue any interest or penalties with respect to uncertain tax positions, which, if applicable, would be recorded as an income tax expense on the Statement of Operations. Tax returns filed within the prior three years remain subject to examination by federal and state tax authorities.

The amount and character of income and capital gain distributions to shareowners are determined in accordance with federal income tax rules, which may differ from U.S. GAAP. Distributions in excess of net investment income or net realized gains are temporary over distributions for financial statement purposes resulting from differences in the recognition or classification of income or distributions for financial statement and tax purposes. Capital accounts within the financial statements are adjusted for permanent book/tax differences to reflect tax character, but are not adjusted for temporary differences.

The tax character of distributions paid during the years ended December 31, 2021 and December 31, 2020, were as follows:

	2021	2020
Distributions paid from:
Ordinary income	$55,605	$491,247
Total distributions	$55,605	$491,247

The following shows the components of distributable earnings (losses) on a federal income tax basis at December 31, 2021:

	2021
Distributable earnings/(losses):
Undistributed ordinary income	$55,851
Undistributed long term capital gain	1,527
Unrealized appreciation/(depreciation)	(218)
Total	$57,160

The difference between book-basis and tax-basis net unrealized appreciation/(depreciation) are attributable to the tax deferral of losses on wash sales.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 25

D. Fund Shares

The Fund records sales and repurchases of its shares as of trade date. The Fund declares as daily dividends substantially all of its net investment income. All dividends are paid on a monthly basis. Short-term capital gain distributions, if any, may be declared with the daily dividends.

E. Class Allocations

Income, common expenses and realized and unrealized gains and losses are calculated at the Fund level and allocated daily to each class of shares based on its respective percentage of adjusted net assets at the beginning of the day.

Distribution fees are calculated based on the average daily net asset value attributable to Class A and Class R shares of the Fund, respectively (see Note 4). Class Y shares do not pay distribution fees. All expenses and fees paid to the Fund’s transfer agent for its services are allocated among the classes of shares based on the number of accounts in each class and the ratable allocation of related out-of-pocket expenses (see Note 4).

Distributions to shareowners are recorded as of the ex-dividend date. Distributions paid by the Fund with respect to each class of shares are calculated in the same manner and at the same time, except that net investment income dividends to Class A, Class R and Class Y shares can reflect different transfer agent and distribution expense rates.

F. Risks

Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. It is possible to lose money by investing in the Fund. Fund shares are not federally insured by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support at any time.

At times, the Fund’s investments may represent industries or industry sectors that are interrelated or have common risks, making the Fund more susceptible to any economic, political, or regulatory developments or other risks affecting those industries and sectors. The value of assets or income from investment may be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the Fund’s assets can decline as can the value of the Fund’s distributions.

26 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

The Fund’s investments, payment obligations and financing terms may be based on floating rates, such as LIBOR (London Interbank Offered Rate). Plans are underway to phase out the use of LIBOR. The UK Financial Conduct Authority (“FCA”) and LIBOR’s administrator, ICE Benchmark Administration (“IBA”), have announced that most LIBOR rates will no longer be published after the end of 2021 and a majority of U.S. dollar LIBOR rates will no longer be published after June 30, 2023. It is possible that the FCA may compel the IBA to publish a subset of LIBOR settings after these dates on a “synthetic” basis, but any such publications would be considered non-representative of the underlying markets. Actions by regulators have resulted in the establishment of alternative reference rates to LIBOR in most major currencies. Based on the recommendations of the New York Federal Reserve’s Alternative Reference Rate Committee (comprised of major derivative market participants and their regulators), the U.S. Federal Reserve began publishing a Secured Overnight Funding Rate (“SOFR”) that is intended to replace U.S. Dollar LIBOR. Proposals for alternative reference rates for other currencies have also been announced or have already begun publication, such as SONIA in the United Kingdom. Markets are slowly developing in response to these new rates, and transition planning is at a relatively early stage. Neither the effect of the transition process nor its ultimate success is known. The transition process may lead to increased volatility and illiquidity in markets that currently rely on LIBOR to determine interest rates. The effect of any changes to — or discontinuation of — LIBOR on the portfolio will vary depending on, among other things, provisions in individual contracts and whether, how, and when industry participants develop and adopt new reference rates and alternative reference rates for both legacy and new products and instruments. Because the usefulness of LIBOR as a benchmark may deteriorate during the transition period, these effects could occur at any time.

With the increased use of technologies such as the Internet to conduct business, the Fund is susceptible to operational, information security and related risks. While the Fund’s Adviser has established business continuity plans in the event of, and risk management systems to prevent, limit or mitigate, such cyber-attacks, there are inherent limitations in such plans and systems, including the possibility that certain risks have not been identified. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by service providers to the Fund such as the Fund’s custodian and accounting agent, and the Fund’s transfer agent. In addition, many beneficial owners of Fund shares hold them through accounts at broker-dealers, retirement platforms and other financial market participants over which neither the

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 27

Fund nor the Adviser exercises control. Each of these may in turn rely on service providers to them, which are also subject to the risk of cyber-attacks. Cybersecurity failures or breaches at the Adviser or the Fund’s service providers or intermediaries have the ability to cause disruptions and impact business operations, potentially resulting in financial losses, interference with the Fund’s ability to calculate its net asset value, impediments to trading, the inability of Fund shareowners to effect share purchases, redemptions or exchanges or receive distributions, loss of or unauthorized access to private shareowner information and violations of applicable privacy and other laws, regulatory fines, penalties, reputational damage, or additional compliance costs. Such costs and losses may not be covered under any insurance. In addition, maintaining vigilance against cyber-attacks may involve substantial costs over time, and system enhancements may themselves be subject to cyber-attacks.

COVID-19

The global pandemic of the novel coronavirus respiratory disease designated COVID-19 has resulted in major disruption to economies and markets around the world, including the United States. Global financial markets have experienced extreme volatility and severe losses, and trading in many instruments has been disrupted. Liquidity for many instruments has been greatly reduced for periods of time. Some interest rates are very low and in some cases yields are negative. Some sectors of the economy and individual issuers have experienced particularly large losses. Rates of inflation have recently risen. These circumstances may continue for an extended period of time, and may continue to affect adversely the value and liquidity of the Fund’s investments. Governments and central banks, including the Federal Reserve in the U.S., have taken extraordinary and unprecedented actions to support local and global economies and the financial markets. These actions have resulted in significant expansion of public debt, including in the U.S. The impact of these measures will not be known for some time. The consequences of high public debt, including its future impact on the economy and securities markets, likewise may not be known for some time.

The Fund’s prospectus contains unaudited information regarding the Fund’s principal risks. Please refer to that document when considering the Fund’s principal risks.

28 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

G. Repurchase Agreements

Repurchase agreements are arrangements under which the Fund purchases securities from a broker-dealer or a bank, called the counterparty, upon the agreement of the counterparty to repurchase the securities from the Fund at a later date, and at a specific price, which is typically higher than the purchase price paid by the Fund. The securities purchased serve as the Fund’s collateral for the obligation of the counterparty to repurchase the securities. The value of the collateral, including accrued interest, is required to be equal to or in excess of the repurchase price. The collateral for all repurchase agreements is held in safekeeping in the customer-only account of the Fund’s custodian or a sub-custodian of the Fund. The Adviser is responsible for determining that the value of the collateral remains at least equal to the repurchase price. In the event of a default by the counterparty, the Fund is entitled to sell the securities, but the Fund may not be able to sell them for the price at which they were purchased, thus causing a loss to the Fund. Additionally, if the counterparty becomes insolvent, there is some risk that the Fund will not have a right to the securities, or the immediate right to sell the securities.

Open repurchase agreements at December 31, 2021, are disclosed in the Schedule of Investments.

2. Management Agreement

The Adviser manages the Fund’s portfolio. Management fees payable under the Fund’s Investment Management Agreement with the Adviser are calculated daily and paid monthly at the annual rate of 0.35% of the Fund’s average daily net assets up to $1 billion and 0.30% of the Fund’s average daily net assets over $1 billion. For the year ended December 31, 2021, the net management fee (excluding waivers and/or reimbursement of expenses) was equivalent to 0.35% of the Fund’s average daily net assets.

The Adviser has agreed to limit the Fund’s expenses for any class of shares or waive a portion of its management fee in an effort to maintain a net asset value of $1.00 per share. From time to time, the Adviser and its affiliates may limit the expenses of one or more classes for the purpose of avoiding a negative yield or increasing its yield during the period of the limitation. Additionally, the Distributor has voluntarily agreed to waive distribution fees payable by Class A shares. These expense limitation policies are voluntary and temporary and may be revised or terminated by the Adviser or Distributor, as applicable, at any time without notice. Fees waived and expenses reimbursed during the year ended December 31, 2021 are reflected on the Statement of Operations.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 29

In addition, under the management and administration agreements, certain other services and costs, including accounting, regulatory reporting and insurance premiums, are paid by the Fund as administrative reimbursements. Included in “Due to affiliates” reflected on the Statement of Assets and Liabilities is $8,482 in management fees, administrative costs and certain other reimbursements payable to the Adviser at December 31, 2021.

3. Compensation of Trustees and Officers

The Fund pays an annual fee to its Trustees. The Adviser reimburses the Fund for fees paid to the Interested Trustees. For the year ended December 31, 2021, the Fund paid $10,526 in Trustees’ compensation, which is reflected on the Statement of Operations as Trustees’ fees. At December 31, 2021, the Fund had a payable for Trustees’ fees on its Statement of Assets and Liabilities of $1,037.

4. Transfer Agent

For the period from January 1, 2021 to November 21, 2021, DST Asset Manager Solutions, Inc. served as the transfer agent to the Fund at negotiated rates. Effective November 22, 2021, BNY Mellon Investment Servicing (US) Inc. serves as the transfer agent to the Fund at negotiated rates. Transfer agent fees and payables shown on the Statement of Operations and the Statement of Assets and Liabilities, respectively, include sub-transfer agent expenses incurred through the Fund’s omnibus relationship contracts.

In addition, the Fund reimbursed the transfer agent for out-of-pocket expenses incurred by the transfer agent related to shareowner communications activities such as proxy and statement mailings, and outgoing phone calls. For the year ended December 31, 2021, such out-of-pocket expenses by class of shares were as follows:

Shareowner Communications:
Class A	$108,160
Class R	588
Class Y	338
Total	$109,086

30 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

5. Distribution and Service Plans

The Fund has adopted a distribution plan (the “Plan”) pursuant to Rule 12b-1 of the Investment Company Act of 1940 with respect to its Class A and Class R shares. Pursuant to the Plan, the Fund pays the Distributor 0.15% of the average daily net assets attributable to Class A shares as compensation for personal services and/or account maintenance services or distribution services with regard to Class A shares. Pursuant to the Plan, the Fund further pays the Distributor 0.50% of the average daily net assets attributable to Class R shares for distribution services. Included in “Due to affiliates” reflected on the Statement of Assets and Liabilities is $18,503 in distribution fees payable to the Distributor, at December 31, 2021.

The Fund also has adopted a separate service plan for Class R shares (the “Service Plan”). The Service Plan authorizes the Fund to pay securities dealers, plan administrators or other service organizations that agree to provide certain services to retirement plans or plan participants holding shares of the Fund a service fee of up to 0.25% of the Fund’s average daily net assets attributable to Class R shares held by such plans.

6. Changes in Custodian and Sub-Administrator, and Transfer Agent

Effective November 22, 2021, The Bank of New York Mellon Corporation (“BNY Mellon”) serves as the Fund’s Custodian and Sub-Administrator.

Effective November 22, 2021, BNY Mellon Investment Servicing (US) Inc. serves as the Fund’s shareholder servicing and transfer agent.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 31

Report of Independent Registered Public Accounting Firm

To the Board of Trustees of Pioneer Money Market Trust and the Shareholders of Pioneer U.S. Government Money Market Fund:

Opinion on the Financial Statements

We have audited the accompanying statement of assets and liabilities of Pioneer U.S. Government Money Market Fund (the “Fund”) (one of the funds constituting Pioneer Money Market Trust (the “Trust”)), including the schedule of investments, as of December 31, 2021, and the related statement of operations for the year then ended, the statements of changes in net assets for each of the two years in the period then ended, the financial highlights for each of the five years in the period then ended and the related notes (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Pioneer U.S. Government Money Market Fund (one of the funds constituting Pioneer Money Market Trust) at December 31, 2021, the results of its operations for the year then ended, the changes in its net assets for each of the two years in the period then ended, and its financial highlights for each of the five years in the period then ended in conformity with U.S. generally accepted accounting principles.

Basis for Opinion

These financial statements are the responsibility of the Trust’s management. Our responsibility is to express an opinion on the Fund’s financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“PCAOB”) and are required to be independent with respect to the Trust in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Trust is not required to have, nor were we engaged to perform, an audit of the Trust’s internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting, but not for the purpose of expressing an opinion on the effectiveness of the Trust’s internal control over financial reporting. Accordingly, we express no such opinion.

32 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our procedures included confirmation of securities owned as of December 31, 2021, by correspondence with the custodian and brokers or by other appropriate auditing procedures where replies from brokers were not received. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

We have served as the auditor of one or more investment companies in the Pioneer family of funds since 2017.

Boston, Massachusetts
March 1, 2022

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 33

Additional Information (unaudited)

The percentage of the Fund’s ordinary income distributions that are exempt from nonresident alien (NRA) tax withholding resulting from qualified interest income was 100%.

34 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Approval of Renewal of Investment Management Agreement

Amundi Asset Management US, Inc. (“Amundi US”) serves as the investment adviser to Pioneer U.S. Government Money Market Fund (the “Fund”) pursuant to an investment management agreement between Amundi US and the Fund. In order for Amundi US to remain the investment adviser of the Fund, the Trustees of the Fund, including a majority of the Fund’s Independent Trustees, must determine annually whether to renew the investment management agreement for the Fund.

The contract review process began in January 2021 as the Trustees of the Fund agreed on, among other things, an overall approach and timeline for the process. Contract review materials were provided to the Trustees in March 2021, July 2021 and September 2021. In addition, the Trustees reviewed and discussed the Fund’s performance at regularly scheduled meetings throughout the year, and took into account other information related to the Fund provided to the Trustees at regularly scheduled meetings, in connection with the review of the Fund’s investment management agreement.

In March 2021, the Trustees, among other things, discussed the memorandum provided by Fund counsel that summarized the legal standards and other considerations that are relevant to the Trustees in their deliberations regarding the renewal of the investment management agreement, and reviewed and discussed the qualifications of the investment management teams for the Fund, as well as the level of investment by the Fund’s portfolio managers in the Fund. In July 2021, the Trustees, among other things, reviewed the Fund’s management fees and total expense ratios, the financial statements of Amundi US and its parent companies, profitability analyses provided by Amundi US, and analyses from Amundi US as to possible economies of scale. The Trustees also reviewed the profitability of the institutional business of Amundi US as compared to that of Amundi US’s fund management business, and considered the differences between the fees and expenses of the Fund and the fees and expenses of Amundi institutional accounts, as well as the different services provided by Amundi US to the Fund and to the institutional accounts. The Trustees further considered contract review materials, including additional materials received in response to the Trustees’ request, in September 2021.

At a meeting held on September 21, 2021, based on their evaluation of the information provided by Amundi US and third parties, the Trustees of the Fund, including the Independent Trustees voting separately, unanimously approved the renewal of the investment management agreement for another

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 35

year. In approving the renewal of the investment management agreement, the Trustees considered various factors that they determined were relevant, including the factors described below. The Trustees did not identify any single factor as the controlling factor in determining to approve the renewal of the agreement.

Nature, Extent and Quality of Services

The Trustees considered the nature, extent and quality of the services that had been provided by Amundi US to the Fund, taking into account the investment objective and strategy of the Fund. The Trustees also reviewed Amundi US’s investment approach for the Fund and its research process. The Trustees considered the resources of Amundi US and the personnel of Amundi US who provide investment management services to the Fund. They also reviewed the amount of non-Fund assets managed by the portfolio managers of the Fund. They considered the non-investment resources and personnel of Amundi US that are involved in Amundi US’s services to the Fund, including Amundi US’s compliance, risk management, and legal resources and personnel. The Trustees noted the substantial attention and high priority given by Amundi US’s senior management to the Pioneer Fund complex. The Trustees considered the effectiveness of Amundi US’s business continuity plan in response to the COVID-19 pandemic.

The Trustees considered that Amundi US supervises and monitors the performance of the Fund’s service providers and provides the Fund with personnel (including Fund officers) and other resources that are necessary for the Fund’s business management and operations. The Trustees also considered that, as administrator, Amundi US is responsible for the administration of the Fund’s business and other affairs. The Trustees considered Amundi US’s oversight of the process for transitioning custodian, transfer agent and sub-administration services to new service providers. The Trustees considered that the Fund reimburses Amundi US its pro rata share of Amundi US’s costs of providing administration services to the Pioneer Funds.

Based on these considerations, the Trustees concluded that the nature, extent and quality of services that had been provided by Amundi US to the Fund were satisfactory and consistent with the terms of the investment management agreement.

Performance of the Fund

In considering the Fund’s performance, the Trustees regularly review and discuss throughout the year data prepared by Amundi US and information comparing the Fund’s performance with the performance of its peer group

36 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

of funds, as classified by Morningstar, Inc. (Morningstar), and with the performance of the Fund’s benchmark index. They also discuss the Fund’s performance with Amundi US on a regular basis. The Trustees’ regular reviews and discussions were factored into the Trustees’ deliberations concerning the renewal of the investment management agreement.

Management Fee and Expenses

The Trustees considered information showing the fees and expenses of the Fund in comparison to the management fees of its peer group of funds as classified by Morningstar and also to the expense ratios of a peer group of funds selected on the basis of criteria determined by the Independent Trustees for this purpose using data provided by Strategic Insight Mutual Fund Research and Consulting, LLC (Strategic Insight), an independent third party. The peer group comparisons referred to below are organized in quintiles. Each quintile represents one-fifth of the peer group. In all peer group comparisons referred to below, first quintile is most favorable to the Fund’s shareowners. The Trustees noted that they separately review and consider the impact of the Fund’s transfer agency and Fund- and Amundi US-paid expenses for sub-transfer agency and intermediary arrangements, and that the results of the most recent such review were considered in the consideration of the Fund’s expense ratio.

The Trustees considered that the Fund’s management fee for the most recent fiscal year was in the fifth quintile relative to the management fees paid by other funds in its Morningstar category for the comparable period. The Trustees noted Amundi US’s explanation of the reasons that the Fund’s management fee was in the fifth quintile relative to the management fees paid by other funds in its Morningstar category. The Trustees considered that the expense ratio of the Fund’s Class Y shares for the most recent fiscal year was in the first quintile relative to its Strategic Insight peer group for the comparable period. The Trustees considered that the expense ratio of the Fund’s Class A shares for the most recent fiscal year was in the first quintile relative to its Strategic Insight peer group for the comparable period. The Trustees noted that Amundi US had agreed to waive fees and/or reimburse expenses in order to limit the ordinary operating expenses of the Fund.

The Trustees reviewed management fees charged by Amundi US to institutional and other clients, including publicly offered European funds sponsored by Amundi US’s affiliates, unaffiliated U.S. registered investment companies (in a sub-advisory capacity), and unaffiliated foreign and domestic separate accounts. The Trustees also considered Amundi US’s costs in providing services to the Fund and Amundi US’s costs in providing services to the other clients and considered the differences in management

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 37

fees and profit margins for fund and non-fund services. In evaluating the fees associated with Amundi US’s client accounts, the Trustees took into account the respective demands, resources and complexity associated with the Fund and other client accounts. The Trustees noted that, in some instances, the fee rates for those clients were lower than the management fee for the Fund and considered that, under the investment management and administration agreements with the Fund, Amundi US performs additional services for the Fund that it does not provide to those other clients or services that are broader in scope, including oversight of the Fund’s other service providers and activities related to compliance and the extensive regulatory and tax regimes to which the Fund is subject. The Trustees also considered the entrepreneurial risks associated with Amundi US’s management of the Fund.

The Trustees concluded that the management fee payable by the Fund to Amundi US was reasonable in relation to the nature and quality of the services provided by Amundi US.

Profitability

The Trustees considered information provided by Amundi US regarding the profitability of Amundi US with respect to the advisory services provided by Amundi US to the Fund, including the methodology used by Amundi US in allocating certain of its costs to the management of the Fund. The Trustees also considered Amundi US’s profit margin in connection with the overall operation of the Fund. They further reviewed the financial results, including the profit margins, realized by Amundi US from non-fund businesses. The Trustees considered Amundi US’s profit margins in comparison to the limited industry data available and noted that the profitability of any adviser was affected by numerous factors, including its organizational structure and method for allocating expenses. The Trustees concluded that Amundi US’s profitability with respect to the management of the Fund was not unreasonable.

Economies of Scale

The Trustees considered Amundi US’s views relating to economies of scale in connection with the Pioneer Funds as fund assets grow and the extent to which any such economies of scale are shared with the Fund and Fund shareholders. The Trustees recognize that economies of scale are difficult to identify and quantify, and that, among other factors that may be relevant, are the following: fee levels, expense subsidization, investment by Amundi US in research and analytical capabilities and Amundi US’s commitment and resource allocation to the Fund. The Trustees noted that profitability

38 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

also may be an indicator of the availability of any economies of scale, although profitability may vary for other reasons including due to reductions in expenses. The Trustees concluded that economies of scale, if any, were being appropriately shared with the Fund.

Other Benefits

The Trustees considered the other benefits that Amundi US enjoys from its relationship with the Fund. The Trustees considered the character and amount of fees paid or to be paid by the Fund, other than under the investment management agreement, for services provided by Amundi US and its affiliates. The Trustees further considered the revenues and profitability of Amundi US’s businesses other than the Fund business. To the extent applicable, the Trustees also considered the benefits to the Fund and to Amundi US and its affiliates from the use of “soft” commission dollars generated by the Fund to pay for research and brokerage services.

The Trustees considered that Amundi US is the principal U.S. asset management business of Amundi, which is one of the largest asset managers globally. Amundi’s worldwide asset management business manages over $2.12 trillion in assets (including the Pioneer Funds). The Trustees considered that Amundi US’s relationship with Amundi creates potential opportunities for Amundi US and Amundi that derive from Amundi US’s relationships with the Fund, including Amundi’s ability to market the services of Amundi US globally. The Trustees noted that Amundi US has access to additional research and portfolio management capabilities as a result of its relationship with Amundi and Amundi’s enhanced global presence that may contribute to an increase in the resources available to Amundi US. The Trustees considered that Amundi US and the Fund receive reciprocal intangible benefits from the relationship, including mutual brand recognition and, for the Fund, direct and indirect access to the resources of a large global asset manager. The Trustees concluded that any such benefits received by Amundi US as a result of its relationship with the Fund were reasonable.

Conclusion

After consideration of the factors described above as well as other factors, the Trustees, including the Independent Trustees, concluded that the investment management agreement for the Fund, including the fees payable thereunder, was fair and reasonable and voted to approve the proposed renewal of the investment management agreement.

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 39

Trustees, Officers and Service ProvidersInvestment Adviser and AdministratorAmundi Asset Management US, Inc.Custodian and Sub-AdministratorThe Bank of New York Mellon CorporationIndependent Registered Public Accounting FirmErnst & Young LLPPrincipal UnderwriterAmundi Distributor US, Inc.Legal CounselMorgan, Lewis & Bockius LLPTransfer AgentBNY Mellon Investment Servicing (US) Inc.

Proxy Voting Policies and Procedures of the Fund are available without charge, upon request, by calling our toll free number (1-800-225-6292). Information regarding how the Fund voted proxies relating to portfolio securities during the most recent 12-month period ended June 30 is publicly available to shareowners at www.amundi.com/us. This information is also available on the Securities and Exchange Commission’s web site at www.sec.gov.

Trustees and Officers

The Fund’s Trustees and officers are listed below, together with their principal occupations and other directorships they have held during at least the past five years. Trustees who are interested persons of the Fund within the meaning of the 1940 Act are referred to as Interested Trustees. Trustees who are not interested persons of the Fund are referred to as Independent Trustees. Each of the Trustees serves as a Trustee of each of the 49 U.S. registered investment portfolios for which Amundi US serves as investment adviser (the “Pioneer Funds”). The address for all Trustees and all officers of the Fund is 60 State Street, Boston, Massachusetts 02109.

The Statement of Additional Information of the Fund includes additional information about the Trustees and is available, without charge, upon request, by calling 1-800-225-6292.

40 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Independent Trustees

			Other Directorships
Name, Age and Position	Term of Office and		Held by Trustee During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Thomas J. Perna (71)	Trustee since 2006.	Private investor (2004 – 2008 and 2013 – present); Chairman (2008 – 2013)	Director, Broadridge Financial
Chairman of the Board	Serves until a successor	and Chief Executive Officer (2008 – 2012), Quadriserv, Inc. (technology	Solutions, Inc. (investor
and Trustee	trustee is elected or	products for securities lending industry); and Senior Executive Vice	communications and securities
	earlier retirement	President, The Bank of New York (financial and securities services)	processing provider for financial
	or removal.	(1986 – 2004)	services industry) (2009 – present);
			Director, Quadriserv, Inc. (2005 –
			2013); and Commissioner, New
			Jersey State Civil Service
			Commission (2011 – 2015)
John E. Baumgardner, Jr. (70)	Trustee since 2019.	Of Counsel (2019 – present), Partner (1983-2018), Sullivan & Cromwell	Chairman, The Lakeville Journal
Trustee	Serves until a successor	LLP (law firm).	Company, LLC, (privately-held
	trustee is elected or		community newspaper group)
	earlier retirement		(2015-present)
	or removal.
Diane Durnin (64)	Trustee since 2019.	Managing Director - Head of Product Strategy and Development, BNY	None
Trustee	Serves until a successor	Mellon Investment Management (investment management firm) (2012-2018);
	trustee is elected or	Vice Chairman – The Dreyfus Corporation (2005 – 2018): Executive Vice
	earlier retirement	President Head of Product, BNY Mellon Investment Management (2007-2012);
	or removal.	Executive Director- Product Strategy, Mellon Asset Management (2005-2007);
		Executive Vice President Head of Products, Marketing and Client Service,
		Dreyfus Corporation (investment management firm) (2000-2005); and Senior
		Vice President Strategic Product and Business Development, Dreyfus
		Corporation (1994-2000)

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 41

Independent Trustees (continued)

			Other Directorships
Name, Age and Position	Term of Office and		Held by Trustee During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Benjamin M. Friedman (77)	Trustee since 2008.	William Joseph Maier Professor of Political Economy, Harvard University	Trustee, Mellon Institutional Funds
Trustee	Serves until a successor	(1972 – present)	Investment Trust and Mellon
	trustee is elected or		Institutional Funds Master Portfolio
	earlier retirement		(oversaw 17 portfolios in fund
	or removal.		complex) (1989 - 2008)
Craig C. MacKay (58)	Trustee since 2021.	Partner, England & Company, LLC (advisory firm) (2012 – present); Group	Board Member of Carver Bancorp,
Trustee	Serves until a successor	Head – Leveraged Finance Distribution, Oppenheimer & Company	Inc. (holding company) and Carver
	trustee is elected or	(investment bank) (2006 – 2012); Group Head – Private Finance & High	Federal Savings Bank, NA (2017 –
	earlier retirement	Yield Capital Markets Origination, SunTrust Robinson Humphrey (investment	present); Advisory Council Member,
	or removal.	bank) (2003 – 2006); and Founder and Chief Executive Officer, HNY	MasterShares ETF (2016 – 2017);
		Associates, LLC (investment bank) (1996 – 2003)	Advisory Council Member, The Deal
			(financial market information
			publisher) (2015 – 2016); Board Co-
			Chairman and Chief Executive
			Officer, Danis Transportation
			Company (privately-owned
			commercial carrier) (2000 – 2003);
			Board Member and Chief Financial
			Officer, Customer Access Resources
			(privately-owned teleservices
			company) (1998 – 2000); Board
			Member, Federation of Protestant
			Welfare Agencies (human services
			agency) (1993 – present); and
			Board Treasurer, Harlem Dowling
			Westside Center (foster care
			agency) (1999 – 2018)

42 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

			Other Directorships
Name, Age and Position	Term of Office and		Held by Trustee During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Lorraine H. Monchak (65)	Trustee since 2017.	Chief Investment Officer, 1199 SEIU Funds (healthcare workers union	None
Trustee	(Advisory Trustee from	pension funds) (2001 – present); Vice President – International Investments
	2014 - 2017). Serves until	Group, American International Group, Inc. (insurance company)
	a successor trustee is	(1993 – 2001); Vice President – Corporate Finance and Treasury Group,
	elected or earlier	Citibank, N.A. (1980 – 1986 and 1990 – 1993); Vice President – Asset/Liability
	retirement or removal.	Management Group, Federal Farm Funding Corporation (government-
		sponsored issuer of debt securities) (1988 – 1990); Mortgage Strategies
		Group, Shearson Lehman Hutton, Inc. (investment bank) (1987 – 1988);
		and Mortgage Strategies Group, Drexel Burnham Lambert, Ltd. (investment
		bank) (1986 – 1987)
Marguerite A. Piret (73)	Trustee since 1987.	Chief Financial Officer, American Ag Energy, Inc. (controlled environment	Director of New America High
Trustee	Serves until a successor	and agriculture company) (2016 – present); and President and Chief	Income Fund, Inc. (closed-end
	trustee is elected or	Executive Officer, Metric Financial Inc. (formerly known as Newbury Piret	investment company) (2004 –
	earlier retirement	Company) (investment banking firm) (1981 – 2019)	present); and Member, Board of
	or removal.		Governors, Investment Company
			Institute (2000 – 2006)
Fred J. Ricciardi (74)	Trustee since 2014.	Private investor (2020 – present); Consultant (investment company services)	None
Trustee	Serves until a successor	(2012 – 2020); Executive Vice President, BNY Mellon (financial and investment
	trustee is elected or	company services) (1969 – 2012); Director, BNY International Financing Corp.
	earlier retirement	(financial services) (2002 – 2012); Director, Mellon Overseas Investment Corp.
	or removal.	(financial services) (2009 – 2012); Director, Financial Models (technology)
		(2005-2007); Director, BNY Hamilton Funds, Ireland (offshore investment
		companies) (2004-2007); Chairman/Director, AIB/BNY Securities Services,
		Ltd., Ireland (financial services) (1999-2006); and Chairman, BNY Alternative
		Investment Services, Inc. (financial services) (2005-2007)

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 43

Interested Trustees

			Other Directorships
Name, Age and Position	Term of Office and		Held by Trustee During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Lisa M. Jones (59)*	Trustee since 2017.	Director, CEO and President of Amundi US, Inc. (investment management	None
Trustee, President and	Serves until a successor	firm) (since September 2014); Director, CEO and President of Amundi Asset
Chief Executive Officer	trustee is elected or	Management US, Inc. (since September 2014); Director, CEO and President
	earlier retirement	of Amundi Distributor US, Inc. (since September 2014); Director, CEO and
	or removal	President of Amundi Asset Management US, Inc. (since September 2014);
		Chair, Amundi US, Inc., Amundi Distributor US, Inc. and Amundi Asset
		Management US, Inc. (September 2014 – 2018); Managing Director, Morgan
		Stanley Investment Management (investment management firm)
		(2010 – 2013); Director of Institutional Business, CEO of International, Eaton
		Vance Management (investment management firm) (2005 – 2010); and
		Director of Amundi Holdings US, Inc. (since 2017)
Kenneth J. Taubes (63)*	Trustee since 2014.	Director and Executive Vice President (since 2008) and Chief Investment	None
Trustee	Serves until a successor	Officer, U.S. (since 2010) of Amundi US, Inc. (investment management firm);
	trustee is elected or	Director and Executive Vice President and Chief Investment Officer, U.S. of
	earlier retirement	Amundi US (since 2008); Executive Vice President and Chief Investment
	or removal	Officer, U.S. of Amundi Asset Management US, Inc. (since 2009); Portfolio
		Manager of Amundi US (since 1999); and Director of Amundi Holdings US,
		Inc. (since 2017)

* Ms. Jones and Mr. Taubes are Interested Trustees because they are officers or directors of the Fund’s investment adviser and certain of its affiliates.

44 Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21

Fund Officers

			Other Directorships
Name, Age and Position	Term of Office and		Held by Officer During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Christopher J. Kelley (57)	Since 2003. Serves at the	Vice President and Associate General Counsel of Amundi US since	None
Secretary and Chief	discretion of the Board	January 2008; Secretary and Chief Legal Officer of all of the Pioneer Funds
Legal Officer		since June 2010; Assistant Secretary of all of the Pioneer Funds from
		September 2003 to May 2010; and Vice President and Senior Counsel of
		Amundi US from July 2002 to December 2007
Thomas Reyes (59)	Since 2010. Serves at the	Assistant General Counsel of Amundi US since May 2013 and Assistant	None
Assistant Secretary	discretion of the Board	Secretary of all the Pioneer Funds since June 2010; and Counsel of
		Amundi US from June 2007 to May 2013
Anthony J. Koenig, Jr. (58)	Since 2021. Serves at the	Senior Vice President – Fund Treasury of Amundi US; Treasurer of all of the	None
Treasurer and Chief Financial	discretion of the Board	Pioneer Funds since May 2021; Assistant Treasurer of all of the Pioneer Funds
and Accounting Officer		from January 2021 to May 2021; and Chief of Staff, US Investment
		Management of Amundi US from May 2008 to January 2021
Luis I. Presutti (56)	Since 2000. Serves at the	Director – Fund Treasury of Amundi US since 1999; and Assistant Treasurer	None
Assistant Treasurer	discretion of the Board	of all of the Pioneer Funds since 1999
Gary Sullivan (63)	Since 2002. Serves at the	Senior Manager – Fund Treasury of Amundi US since 2012; and Assistant	None
Assistant Treasurer	discretion of the Board	Treasurer of all of the Pioneer Funds since 2002
Antonio Furtado (39)	Since 2020. Serves at the	Fund Oversight Manager – Fund Treasury of Amundi US since 2020;	None
Assistant Treasurer	discretion of the Board	Assistant Treasurer of all of the Pioneer Funds since 2020; and Senior Fund
		Treasury Analyst from 2012 - 2020

Pioneer U.S. Government Money Market Fund | Annual Report | 12/31/21 45

Fund Officers (continued)

			Other Directorships
Name, Age and Position	Term of Office and		Held by Officer During
Held With the Fund	Length of Service	Principal Occupation(s) During At Least The Past Five Years	At Least The Past Five Years
Michael Melnick (50)	Since 2021. Serves at the	Vice President - Deputy Fund Treasurer of Amundi US since May 2021;	None
Assistant Treasurer	discretion of the Board	Assistant Treasurer of all of the Pioneer Funds since July 2021; Director of
		Regulatory Reporting of Amundi US from 2001 – 2021; and Director of Tax
		of Amundi US from 2000 - 2001
John Malone (51)	Since 2018. Serves at the	Managing Director, Chief Compliance Officer of Amundi US Asset	None
Chief Compliance Officer	discretion of the Board	Management; Amundi Asset Management US, Inc.; and the Pioneer
		Funds since September 2018; and Chief Compliance Officer of Amundi
		Distributor US, Inc. since January 2014.
Kelly O’Donnell (50)	Since 2006. Serves at the	Vice President – Amundi Asset Management; and Anti-Money Laundering	None
Anti-Money	discretion of the Board	Officer of all the Pioneer Funds since 2006
Laundering Officer

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How to Contact Amundi

We are pleased to offer a variety of convenient ways for you to contact us for assistance or information.

Call us for:
Account Information, including existing accounts,
new accounts, prospectuses, applications
and service forms	1-800-225-6292

FactFoneSM for automated fund yields, prices,
account information and transactions	1-800-225-4321

Retirement plans information 1-800-622-0176

Write to us:

AmundiP.O. Box 9897Providence, RI 02940-8097

Our toll-free fax 1-800-225-4240

Our internet e-mail address	us.askamundi@amundi.com
(for general questions about Amundi only)
Visit our web site: www.amundi.com/us

This report must be preceded or accompanied by a prospectus.

The Fund files a complete schedule of portfolio holdings with the Securities and Exchange Commission for the first and third quarters of each fiscal year as an exhibit to its reports on Form N-PORT. Shareholders may view the filed Form N-PORT by visiting the Commission’s web site at https://www.sec.gov.

Amundi Asset Management US, Inc.
60 State Street
Boston, MA 02109
www.amundi.com/us

Securities offered through Amundi Distributor US, Inc.,
60 State Street, Boston, MA 02109
Underwriter of Pioneer Mutual Funds, Member SIPC
© 2022 Amundi Asset Management US, Inc. 18624-16-0222

ITEM 2. CODE OF ETHICS.

(a) Disclose whether, as of the end of the period covered by the report, the registrant has adopted a code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions, regardless of whether these individuals are employed by the registrant or a third party.  If the registrant has not adopted such a code of ethics, explain why it has not done so.

The registrant has adopted, as of the end of the period covered by this report, a code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer and controller.

(b) For purposes of this Item, the term “code of ethics” means written standards that are reasonably designed to deter wrongdoing and to promote:

(1) Honest and ethical conduct, including the ethical handling of actual or apparent conflicts of interest between personal and professional relationships;

(2) Full, fair, accurate, timely, and understandable disclosure in reports and documents that a registrant files with, or submits to, the Commission and in other public communications made by the registrant;

(3) Compliance with applicable governmental laws, rules, and regulations;

(4) The prompt internal reporting of violations of the code to an appropriate person or persons identified in the code; and

(5) Accountability for adherence to the code.

(c) The registrant must briefly describe the nature of any amendment, during the period covered by the report, to a provision of its code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions, regardless of whether these individuals are employed by the registrant or a third party, and that relates to any element of the code of ethics definition enumerated in paragraph (b) of this Item. The registrant must file a copy of any such amendment as an exhibit pursuant to Item 10(a), unless the registrant has elected to satisfy paragraph (f) of this Item by posting its code of ethics on its website pursuant to paragraph (f)(2) of this Item, or by undertaking to provide its code of ethics to any person without charge, upon request, pursuant to paragraph (f)(3) of this Item.

The registrant has made no amendments to the code of ethics during the period covered by this report.

(d) If the registrant has, during the period covered by the report, granted a waiver, including an implicit waiver, from a provision of the code of ethics to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions, regardless of whether these individuals are employed by the registrant or a third party, that relates to one or more of the items set forth in paragraph (b) of this Item, the registrant must briefly describe the nature of the waiver, the name of the person to whom the waiver was granted, and the date of the waiver.

Not applicable.

(e) If the registrant intends to satisfy the disclosure requirement under paragraph (c) or (d) of this Item regarding an amendment to, or a waiver from, a provision of its code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions and that relates to any element of the code of ethics definition

enumerated in paragraph (b) of this Item by posting such information on its Internet website, disclose the registrant’s Internet address and such intention.

Not applicable.

(f) The registrant must:

(1) File with the Commission, pursuant to Item 12(a)(1), a copy of its code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions, as an exhibit to its annual report on this Form N-CSR (see attachment);

(2) Post the text of such code of ethics on its Internet website and disclose, in its most recent report on this Form N-CSR, its Internet address and the fact that it has posted such code of ethics on its Internet website; or

(3) Undertake in its most recent report on this Form N-CSR to provide to any person without charge, upon request, a copy of such code of ethics and explain the manner in which such request may be made. See Item 10(2)

ITEM 3. AUDIT COMMITTEE FINANCIAL EXPERT.

(a) (1)  Disclose that the registrant’s board of trustees has determined that the registrant either:

(i)  Has at least one audit committee financial expert serving on its audit committee; or

(ii) Does not have an audit committee financial expert serving on its audit committee.

The registrant’s Board of Trustees has determined that the registrant has at least one audit committee financial expert.

(2) If the registrant provides the disclosure required by paragraph (a)(1)(i) of this Item, it must disclose the name of the audit committee financial expert and whether that person is “independent.” In order to be considered “independent” for purposes of this Item, a member of an audit committee may not, other than in his or her capacity as a member of the audit committee, the board of trustees, or any other board committee:

(i)  Accept directly or indirectly any consulting, advisory, or other compensatory fee from the issuer; or

(ii) Be an “interested person” of the investment company as defined in Section 2(a)(19) of the Act (15 U.S.C. 80a-2(a)(19)).

Mr. Fred J. Ricciardi, an independent trustee, is such an audit committee financial expert.

(3) If the registrant provides the disclosure required by paragraph (a)(1) (ii) of this Item, it must explain why it does not have an audit committee financial expert.

Not applicable.

ITEM 4. PRINCIPAL ACCOUNTANT FEES AND SERVICES.

(a) Disclose, under the caption AUDIT FEES, the aggregate fees billed for each of the last two fiscal years for professional services rendered by the principal accountant for the audit of the registrant’s annual financial statements or services that are normally provided by the accountant in connection with statutory and regulatory filings or engagements for those fiscal years.

The audit fees for the Trust were $26,040 payable to Ernst & Young LLP for the year ended December 31, 2021 and $26,040 for the year ended December 31, 2020.

(b) Disclose, under the caption AUDIT-RELATED FEES, the aggregate fees billed in each of the last two fiscal years for assurance and related services by the principal accountant that are reasonably related to the performance of the audit of the registrant’s financial statements and are not reported under paragraph (a) of this Item. Registrants shall describe the nature of the services comprising the fees disclosed under this category.

There were no audit-related services in 2021 or 2020.

(c) Disclose, under the caption TAX FEES, the aggregate fees billed in each of the last two fiscal years for professional services rendered by the principal accountant for tax compliance, tax advice, and tax planning. Registrants shall describe the nature of the services comprising the fees disclosed under this category.

The Trust paid aggregate non-audit fees to Ernst & Young LLP for tax services of $6,915 and $6,915 during the fiscal years ended December 31, 2021 and 2020, respectively.

(d) Disclose, under the caption ALL OTHER FEES, the aggregate fees billed in each of the last two fiscal years for products and services provided by the principal accountant, other than the services reported in paragraphs (a) through (c) of this Item. Registrants shall describe the nature of the services comprising the fees disclosed under this category.

There were no other fees in 2021 or 2020.

(e) (1) Disclose the audit committee’s pre-approval policies and procedures described in paragraph (c)(7) of Rule 2-01 of Regulation S-X.

PIONEER FUNDS

APPROVAL OF AUDIT, AUDIT-RELATED, TAX AND OTHER SERVICES

PROVIDED BY THE INDEPENDENT AUDITOR

SECTION I - POLICY PURPOSE AND APPLICABILITY

The Pioneer Funds recognize the importance of maintaining the independence of their outside auditors. Maintaining independence is a shared responsibility involving Amundi Asset Management US, Inc., the audit committee and the independent auditors.

The Funds recognize that a Fund’s independent auditors: 1) possess knowledge of the Funds, 2) are able to incorporate certain services into the scope of the audit, thereby avoiding redundant work, cost and disruption of Fund personnel and processes, and 3) have expertise that has value to the Funds. As a result, there are situations where it is desirable to use the Fund’s independent auditors for services in addition to the annual audit and where the potential for conflicts of interests are minimal. Consequently, this policy, which is intended to comply with Rule 210.2-01(C)(7), sets forth guidelines and procedures to be followed by the Funds when retaining the independent audit firm to perform audit, audit-related tax and other services under those circumstances, while also maintaining independence.

Approval of a service in accordance with this policy for a Fund shall also constitute approval for any other Fund whose pre-approval is required pursuant to Rule 210.2-01(c)(7)(ii).

In addition to the procedures set forth in this policy, any non-audit services that may be provided consistently with Rule 210.2-01 may be approved by the Audit Committee itself and any pre-approval that may be waived in accordance with Rule 210.2-01(c)(7)(i)(C) is hereby waived.

Selection of a Fund’s independent auditors and their compensation shall be determined by the Audit Committee and shall not be subject to this policy.

SECTION II - POLICY
SERVICE CATEGORY	SERVICE CATEGORY DESCRIPTION		SPECIFIC PRE-APPROVED SERVICE SUBCATEGORIES
I. AUDIT SERVICES	Services that are directly		o Accounting research assistance
	related to performing the		o SEC consultation, registration
	independent audit of the Funds		statements, and reporting
			o Tax accrual related matters
			o Implementation of new accounting standards
			o Compliance letters (e.g. rating agency letters)
			o Regulatory reviews and assistance
			regarding financial matters
			o Semi-annual reviews (if requested)
			o Comfort letters for closed end offerings
II. AUDIT-RELATED	Services which are not		o AICPA attest and agreed-upon procedures
SERVICES	prohibited under Rule		o Technology control assessments
	210.2-01(C)(4) (the “Rule”)		o Financial reporting control assessments
	and are related extensions of		o Enterprise security architecture
	the audit services support the		assessment
	audit, or use the knowledge/expertise
	gained from the audit procedures as a
	foundation to complete the project.
	In most cases, if the Audit-Related
	Services are not performed by the
	Audit firm, the scope of the Audit
	Services would likely increase.
	The Services are typically well-defined
	and governed by accounting
	professional standards (AICPA,
	SEC, etc.)
AUDIT COMMITTEE APPROVAL POLICY		AUDIT COMMITTEE REPORTING POLICY
o “One-time” pre-approval		o A summary of all such
for the audit period for all		services and related fees
pre-approved specific service		reported at each regularly
subcategories. Approval of the		scheduled Audit Committee
independent auditors as		meeting.
auditors for a Fund shall
constitute pre approval for
these services.
o “One-time” pre-approval		o A summary of all such
for the fund fiscal year within		services and related fees
a specified dollar limit		(including comparison to
for all pre-approved		specified dollar limits)
specific service subcategories		reported quarterly.

o Specific approval is 

needed to exceed the 

pre-approved dollar limit for 

these services (see general 

Audit Committee approval policy 

below for details on obtaining 

specific approvals) 

o Specific approval is 

needed to use the Fund’s 

auditors for Audit-Related 

Services not denoted as 

“pre-approved”, or 

to add a specific service 

subcategory as “pre-approved” 

SECTION III - POLICY DETAIL, CONTINUED

SERVICE CATEGORY	SERVICE CATEGORY DESCRIPTION	SPECIFIC PRE-APPROVED SERVICE
		SUBCATEGORIES
III. TAX SERVICES	Services which are not	o Tax planning and support
	prohibited by the Rule,	o Tax controversy assistance
	if an officer of the Fund	o Tax compliance, tax returns, excise
	determines that using the	tax returns and support
	Fund’s auditor to provide	o Tax opinions
	these services creates
	significant synergy in
	the form of efficiency,
	minimized disruption, or
	the ability to maintain a
	desired level of
	confidentiality.

AUDIT COMMITTEE APPROVAL POLICY	AUDIT COMMITTEE REPORTING POLICY
o “One-time” pre-approval	o A summary of
for the fund fiscal year	all such services and
within a specified dollar limit	related fees
	(including comparison
	to specified dollar
	limits) reported
	quarterly.
o Specific approval is
needed to exceed the
pre-approved dollar limits for
these services (see general
Audit Committee approval policy
below for details on obtaining
specific approvals)
o Specific approval is
needed to use the Fund’s
auditors for tax services not
denoted as pre-approved, or to
add a specific service subcategory as
“pre-approved”

SECTION III - POLICY DETAIL, CONTINUED

SERVICE CATEGORY	SERVICE CATEGORY DESCRIPTION	SPECIFIC PRE-APPROVED SERVICE
		SUBCATEGORIES
IV. OTHER SERVICES	Services which are not	o Business Risk Management support
	prohibited by the Rule,	o Other control and regulatory
A. SYNERGISTIC,	if an officer of the Fund	compliance projects
UNIQUE QUALIFICATIONS	determines that using the
	Fund’s auditor to provide
	these services creates
	significant synergy in
	the form of efficiency,
	minimized disruption,
	the ability to maintain a
	desired level of
	confidentiality, or where
	the Fund’s auditors
	posses unique or superior
	qualifications to provide
	these services, resulting
	in superior value and
	results for the Fund.

AUDIT COMMITTEE APPROVAL POLICY	AUDIT COMMITTEE REPORTING POLICY
o “One-time” pre-approval	o A summary of
for the fund fiscal year within	all such services and
a specified dollar limit	related fees
	(including comparison
	to specified dollar
	limits) reported
	quarterly.
o Specific approval is
needed to exceed the
pre-approved dollar limits for
these services (see general
Audit Committee approval policy
below for details on obtaining
specific approvals)
o Specific approval is
needed to use the Fund’s
auditors for “Synergistic” or
“Unique Qualifications” Other
Services not denoted as
pre-approved to the left, or to
add a specific service
subcategory as “pre-approved”

SECTION III - POLICY DETAIL, CONTINUED

SERVICE CATEGORY	SERVICE CATEGORY DESCRIPTION	SPECIFIC PROHIBITED SERVICE
		SUBCATEGORIES
PROHIBITED SERVICES	Services which result	1. Bookkeeping or other services
	in the auditors losing	related to the accounting records or
	independence status	financial statements of the audit
	under the Rule.	client*
		2. Financial information systems design
		and implementation*
		3. Appraisal or valuation services,
		fairness* opinions, or
		contribution-in-kind reports
		4. Actuarial services (i.e., setting
		actuarial reserves versus actuarial
		audit work)*
		5. Internal audit outsourcing services*
		6. Management functions or human
		resources
		7. Broker or dealer, investment
		advisor, or investment banking services
		8. Legal services and expert services
		unrelated to the audit
		9. Any other service that the Public
		Company Accounting Oversight Board
		determines, by regulation, is
		impermissible

AUDIT COMMITTEE APPROVAL POLICY	AUDIT COMMITTEE REPORTING POLICY
o These services are not to be	o A summary of all
performed with the exception of the(*)	services and related
services that may be permitted	fees reported at each
if they would not be subject to audit	regularly scheduled
procedures at the audit client (as	Audit Committee meeting
defined in rule 2-01(f)(4)) level	will serve as continual
the firm providing the service.	confirmation that has
	not provided any
	restricted services.

GENERAL AUDIT COMMITTEE APPROVAL POLICY:

o For all projects, the officers of the Funds and the Fund’s auditors will each make an assessment to determine that any proposed projects will not impair independence.

o Potential services will be classified into the four non-restricted service categories and the “Approval of Audit, Audit-Related, Tax and Other Services” Policy above will be applied. Any services outside the specific pre-approved service subcategories set forth above must be specifically approved by the Audit Committee.

o At least quarterly, the Audit Committee shall review a report summarizing the services by service category, including fees, provided by the Audit firm as set forth in the above policy.

(2) Disclose the percentage of services described in each of paragraphs (b) through (d) of this Item that were approved by the audit committee pursuant to paragraph (c)(7)(i)(C) of Rule 2-01 of Regulation S-X.

Non-Audit Services

Beginning with non-audit service contracts entered into on or after May 6, 2003, the effective date of the

new SEC pre-approval rules, the Trust's audit committee is required to pre-approve services to

affiliates defined by SEC rules to the extent that the services are determined to have a direct impact on the operations or financial reporting of the Trust. For the years ended December 31, 2021 and 2020, there were no services provided to an affiliate that required the Trust's audit committee pre-approval.

(f) If greater than 50 percent, disclose the percentage of hours expended on the principal accountants engagement to audit the registrant’s financial statements for the most recent fiscal year that were attributed to work performed by persons other than the principal accountant’s full-time, permanent employees.

N/A

(g) Disclose the aggregate non-audit fees billed by the registrants accountant for services rendered to the registrant, and rendered to the registrants investment adviser (not including any sub-adviser whose role is primarily portfolio management and is subcontracted with or overseen by another investment adviser), and any entity controlling, controlled by, or under common control with the adviser that provides ongoing services to the registrant for each of the last two fiscal years of the registrant.

The Trust paid aggregate non-audit fees to Ernst & Young LLP for tax services of $6,915 and $6,915 during the fiscal years ended December 31, 2021 and 2020, respectively.

(h) Disclose whether the registrants audit committee of the board of trustees has considered whether the provision of non-audit services that were rendered to the registrants investment adviser (not including any subadviser whose role is primarily portfolio management and is subcontracted with or overseen by another investment adviser), and any entity controlling, controlled by, or under common control with the investment adviser that provides ongoing services to the registrant that were not pre-approved pursuant to paragraph (c)(7)(ii) of Rule 2-01 of Regulation S-X is compatible with maintaining the principal accountant’s independence.

The Fund’s audit committee of the Board of Trustees has considered whether the provision of non-audit services that were rendered to the Affiliates (as defined) that were not pre- approved pursuant to paragraph (c)(7)(ii) of Rule 2-01 of Regulation S-X is compatible with maintaining the principal accountant’s independence.

ITEM 5. AUDIT COMMITTEE OF LISTED REGISTRANTS

(a) If the registrant is a listed issuer as defined in Rule 10A-3 under the Exchange Act (17 CFR 240.10A-3), state whether or not the registrant has a separately-designated standing audit committee established in accordance with Section 3(a)(58)(A) of the Exchange Act (15 U.S.C. 78c(a)(58)(A)). If the registrant has such a committee, however designated, identify each committee member. If the entire board of directors is acting as the registrant’s audit committee as specified in Section 3(a)(58)(B) of the Exchange Act (15 U.S.C. 78c(a)(58)(B)), so state.

N/A

(b) If applicable, provide the disclosure required by Rule 10A-3(d) under the Exchange Act (17 CFR 240.10A-3(d)) regarding an exemption from the listing standards for audit committees.

N/A

ITEM 6. SCHEDULE OF INVESTMENTS.

File Schedule of Investments in securities of unaffiliated issuers as of the close of the reporting period as set forth in 210.1212 of Regulation S-X [17 CFR 210.12-12], unless the schedule is included as part of the report to shareholders filed under Item 1 of this Form.

Included in Item 1

ITEM 7. DISCLOSURE OF PROXY VOTING POLICIES AND PROCEDURES FOR CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

A closed-end management investment company that is filing an annual report on this Form N-CSR must, unless it invests exclusively in non-voting securities, describe the policies and procedures that it uses to determine how to vote proxies relating to portfolio securities, including the procedures that the company uses when a vote presents a conflict between the interests of its shareholders, on the one hand, and those of the company’s investment adviser; principal underwriter; or any affiliated person (as defined in Section 2(a)(3) of the Investment Company Act of 1940 (15 U.S.C. 80a-2(a)(3)) and the rules thereunder) of the company, its investment adviser, or its principal underwriter, on the other. Include any policies and procedures of the company’s investment adviser, or any other third party, that the company uses, or that are used on the company’s behalf, to determine how to vote proxies relating to portfolio securities.

Not applicable to open-end management investment companies.

ITEM 8. PORTFOLIO MANAGERS OF CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

(a) If the registrant is a closed-end management investment company that is filing an annual report on this Form N-CSR, provide the following information:

(1) State the name, title, and length of service of the person or persons employed by or associated with the registrant or an investment adviser of the registrant who are primarily responsible for the day-to-day management of the registrant’s portfolio (“Portfolio Manager”). Also state each Portfolio Manager’s business experience during the past 5 years.

Not applicable to open-end management investment companies.

ITEM 9. PURCHASES OF EQUITY SECURITIES BY CLOSED-END MANAGEMENT INVESTMENT COMPANY AND AFFILIATED PURCHASERS.

(a) If the registrant is a closed-end management investment company, in the following tabular format, provide the information specified in paragraph (b) of this Item with respect to any purchase made by or on behalf of the registrant or any affiliated purchaser, as defined in Rule 10b-18(a)(3) under the Exchange Act (17 CFR 240.10b-18(a)(3)), of shares or other units of any class of the registrant’s equity securities that is registered by the registrant pursuant to Section 12 of the Exchange Act (15 U.S.C. 781).

Not applicable to open-end management investment companies.

ITEM 10. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

Describe any material changes to the procedures by which shareholders may recommend nominees to the registrant’s board of directors, where those changes were implemented after the registrant last provided disclosure in response to the requirements of Item 407(c)(2)(iv) of Regulation S-R(17 CFR 229.407)(as required by Item 22(b)(15)) of Schedule 14A (17 CFR 240.14a-101), or this Item.

There have been no material changes to the procedures by which the shareholders may recommend nominees to the registrant’s board of directors since the registrant last provided disclosure in response to the requirements of Item 407(c)(2)(iv) of Regulation S-R of Schedule 14(A) in its definitive proxy statement, or this item.

ITEM 11. CONTROLS AND PROCEDURES.

(a) Disclose the conclusions of the registrant’s principal executive and principal financials officers, or persons performing similar functions, regarding the effectiveness of the registrant’s disclosure controls and procedures (as defined in Rule 30a-3(c) under the Act (17 CFR 270.30a-3(c))) as of a date within 90 days of the filing date of the report that includes the disclosure required by this paragraph, based on the evaluation of these controls and procedures required by Rule 30a-3(b) under the Act (17 CFR 270.30(a)-3(b) and Rules 13a-15(b) or 15d-15(b) under the Exchange Act (17 CFR 240.13a-15(b) or 240.15d-15(b)).

The registrant’s principal executive officer and principal financial officer have concluded that the registrant’s disclosure controls and procedures are effective based on the evaluation of these controls and procedures as of a date within 90 days of the filing date of this report.

(b) Disclose any change in the registrant’s internal control over financial reporting (as defined in Rule 30a-3(d) under the Act (17CFR 270.30a-3(d)) that occured during the second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

There were no significant changes in the registrant’s internal control over financial reporting that occurred during the second fiscal quarter of the period covered by this report that have materially affected, or are reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 12. Disclosure of Securities Lending Activities for Closed-End Management Investment Companies.

(a) If the registrant is a closed-end management investment company, provide the following dollar amounts of income and compensation related to the securities lending activities of the registrant during its most recent fiscal year:

N/A

(1) Gross income from securities lending activities;

N/A

(2) All fees and/or compensation for each of the following securities lending activities and related services: any share of revenue generated by the securities lending program paid to the securities lending agent(s) (revenue split); fees paid for cash collateral management services (including fees deducted from a pooled cash collateral reinvestment vehicle) that are not included in the revenue split; administrative fees that are not included in the revenue split; fees for indemnification that are not included in the revenue split; rebates paid to borrowers; and any other fees relating to the securities lending program that are not included in the revenue split, including a description of those other fees;

N/A

(3) The aggregate fees/compensation disclosed pursuant to paragraph (2); and

N/A

(4) Net income from securities lending activities (i.e., the dollar amount in paragraph (1) minus the dollar amount in paragraph (3)).

If a fee for a service is included in the revenue split, state that the fee is included in the revenue split.

N/A

(b) If the registrant is a closed-end management investment company, describe the services provided to the registrant by the securities lending agent in the registrants most recent fiscal year.

N/A

ITEM 13. EXHIBITS.

(a) File the exhibits listed below as part of this Form. Letter or number the exhibits in the sequence indicated.

(1) Any code of ethics, or amendment thereto, that is the subject of the disclosure required by Item 2, to the extent that the registrant intends to satisfy the Item 2 requirements through filing of an exhibit.

(2) A separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule 30a-2(a) under the Act (17 CFR 270.30a-2(a)) , exactly as set forth below:

Filed herewith.

SIGNATURES

[See General Instruction F]

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant) Pioneer Money Market Trust

By (Signature and Title)* /s/ Lisa M. Jones

Lisa M. Jones, President and Chief Executive Officer

Date March 8, 2022

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)* /s/ Lisa M. Jones

Lisa M. Jones, President and Chief Executive Officer

Date March 8, 2022

By (Signature and Title)* /s/ Anthony J. Koenig, Jr.

Anthony J. Koenig, Jr., Managing Director, Chief Operations Officer & Treasurer of the Funds

Date March 8, 2022

* Print the name and title of each signing officer under his or her signature.