497

The interactive data file included as an exhibit to this filing relates to the supplements to the prospectuses for Columbia Acorn International Select Fund filed pursuant to Rule 497(e) under the Securities Act of 1933, as amended, on June 28, 2019 (Accession No. 0001193125-19-185965), which is incorporated herein by reference.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2018
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Central Index Key	dei_EntityCentralIndexKey	0000002110
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Jun. 28, 2019
Document Effective Date	dei_DocumentEffectiveDate	Jun. 28, 2019
Prospectus Date	rr_ProspectusDate	May 01, 2019
Entity Inv Company Type	dei_EntityInvCompanyType	N-1A

XML

May 01, 2019

COLUMBIA ACORN TRUST

Supplement dated July 1, 2019

to the Prospectus, Summary Prospectus and Statement of Additional Information (“SAI”) dated May 1, 2019

for following Fund (“Fund”):

Columbia Acorn International Select

Effective immediately, the Fund’s Prospectus and Summary Prospectus are supplemented as follows:

1. The Annual Fund Operating Expenses table that appears under the section heading “Fees and Expenses of the Fund” is removed and replaced with the following:

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.31%	0.26%
Total annual Fund operating expenses(d)	1.53%	1.28%	2.28%	1.28%	1.20%	1.15%
Fee waivers and/or expense reimbursements(e)	(0.22)%	(0.22)%	(0.22)%	(0.22)%	(0.23)%	(0.23)%
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.31%	1.06%	2.06%	1.06%	0.97%	0.92%

^(c)  Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

^(d)  “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

^(e)  Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through June 30, 2020, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.31% for Class A shares, 1.06% for Class Adv shares, 2.06% for Class C shares, 1.06% for Class Inst shares, 0.97% for Class Inst2 shares and 0.92% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through June 30, 2020, such that the Fund’s transfer agency fees do not exceed the annual rates of 0.05% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

2. The Example table and the paragraph that immediately precedes it under the section heading “Fees and Expenses of the Fund” are removed and replaced with the following:

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$701	$1,010	$1,342	$2,276
Class Adv (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class C (assuming redemption of all shares at the end of the period)	$309	$691	$1,200	$2,598
Class C (assuming no redemption of shares)	$209	$691	$1,200	$2,598
Class Inst (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class Inst2 (whether or not shares are redeemed)	$99	$358	$638	$1,434
Class Inst3 (whether or not shares are redeemed)	$94	$343	$611	$1,377

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

COLUMBIA ACORN TRUST

Prospectus Date

rr_ProspectusDate

May 01, 2019

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

COLUMBIA ACORN TRUST

Supplement dated July 1, 2019

to the Prospectus, Summary Prospectus and Statement of Additional Information (“SAI”) dated May 1, 2019

for following Fund (“Fund”):

Columbia Acorn International Select

Effective immediately, the Fund’s Prospectus and Summary Prospectus are supplemented as follows:

1. The Annual Fund Operating Expenses table that appears under the section heading “Fees and Expenses of the Fund” is removed and replaced with the following:

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.31%	0.26%
Total annual Fund operating expenses(d)	1.53%	1.28%	2.28%	1.28%	1.20%	1.15%
Fee waivers and/or expense reimbursements(e)	(0.22)%	(0.22)%	(0.22)%	(0.22)%	(0.23)%	(0.23)%
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.31%	1.06%	2.06%	1.06%	0.97%	0.92%

^(c)  Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

^(d)  “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

^(e)  Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through June 30, 2020, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.31% for Class A shares, 1.06% for Class Adv shares, 2.06% for Class C shares, 1.06% for Class Inst shares, 0.97% for Class Inst2 shares and 0.92% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through June 30, 2020, such that the Fund’s transfer agency fees do not exceed the annual rates of 0.05% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

2. The Example table and the paragraph that immediately precedes it under the section heading “Fees and Expenses of the Fund” are removed and replaced with the following:

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$701	$1,010	$1,342	$2,276
Class Adv (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class C (assuming redemption of all shares at the end of the period)	$309	$691	$1,200	$2,598
Class C (assuming no redemption of shares)	$209	$691	$1,200	$2,598
Class Inst (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class Inst2 (whether or not shares are redeemed)	$99	$358	$638	$1,434
Class Inst3 (whether or not shares are redeemed)	$94	$343	$611	$1,377

Columbia Acorn International Select

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

COLUMBIA ACORN TRUST

Supplement dated July 1, 2019

to the Prospectus, Summary Prospectus and Statement of Additional Information (“SAI”) dated May 1, 2019

for following Fund (“Fund”):

Columbia Acorn International Select

Effective immediately, the Fund’s Prospectus and Summary Prospectus are supplemented as follows:

1. The Annual Fund Operating Expenses table that appears under the section heading “Fees and Expenses of the Fund” is removed and replaced with the following:

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.89%	0.89%	0.89%	0.89%	0.89%	0.89%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.39%	0.39%	0.39%	0.39%	0.31%	0.26%
Total annual Fund operating expenses(d)	1.53%	1.28%	2.28%	1.28%	1.20%	1.15%
Fee waivers and/or expense reimbursements(e)	(0.22)%	(0.22)%	(0.22)%	(0.22)%	(0.23)%	(0.23)%
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.31%	1.06%	2.06%	1.06%	0.97%	0.92%

^(c)  Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

^(d)  “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

^(e)  Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through June 30, 2020, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.31% for Class A shares, 1.06% for Class Adv shares, 2.06% for Class C shares, 1.06% for Class Inst shares, 0.97% for Class Inst2 shares and 0.92% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through June 30, 2020, such that the Fund’s transfer agency fees do not exceed the annual rates of 0.05% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

2. The Example table and the paragraph that immediately precedes it under the section heading “Fees and Expenses of the Fund” are removed and replaced with the following:

Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$701	$1,010	$1,342	$2,276
Class Adv (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class C (assuming redemption of all shares at the end of the period)	$309	$691	$1,200	$2,598
Class C (assuming no redemption of shares)	$209	$691	$1,200	$2,598
Class Inst (whether or not shares are redeemed)	$108	$384	$681	$1,526
Class Inst2 (whether or not shares are redeemed)	$99	$358	$638	$1,434
Class Inst3 (whether or not shares are redeemed)	$94	$343	$611	$1,377

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

June 30, 2020

Expenses Restated to Reflect Current [Text]

rr_ExpensesRestatedToReflectCurrent

Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

“Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

Columbia Acorn International Select | Class A

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.53%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.22%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.31%

1 year

rr_ExpenseExampleYear01

$ 701

3 years

rr_ExpenseExampleYear03

1,010

5 years

rr_ExpenseExampleYear05

1,342

10 years

rr_ExpenseExampleYear10

2,276

1 year

rr_ExpenseExampleNoRedemptionYear01

701

3 years

rr_ExpenseExampleNoRedemptionYear03

1,010

5 years

rr_ExpenseExampleNoRedemptionYear05

1,342

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 2,276

Columbia Acorn International Select | Class Adv

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.28%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.22%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.06%

1 year

rr_ExpenseExampleYear01

$ 108

3 years

rr_ExpenseExampleYear03

384

5 years

rr_ExpenseExampleYear05

681

10 years

rr_ExpenseExampleYear10

1,526

1 year

rr_ExpenseExampleNoRedemptionYear01

108

3 years

rr_ExpenseExampleNoRedemptionYear03

384

5 years

rr_ExpenseExampleNoRedemptionYear05

681

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,526

Columbia Acorn International Select | Class C

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

2.28%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.22%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

2.06%

1 year

rr_ExpenseExampleYear01

$ 309

3 years

rr_ExpenseExampleYear03

691

5 years

rr_ExpenseExampleYear05

1,200

10 years

rr_ExpenseExampleYear10

2,598

1 year

rr_ExpenseExampleNoRedemptionYear01

209

3 years

rr_ExpenseExampleNoRedemptionYear03

691

5 years

rr_ExpenseExampleNoRedemptionYear05

1,200

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 2,598

Columbia Acorn International Select | Class Inst

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.39%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.28%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.22%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

1.06%

1 year

rr_ExpenseExampleYear01

$ 108

3 years

rr_ExpenseExampleYear03

384

5 years

rr_ExpenseExampleYear05

681

10 years

rr_ExpenseExampleYear10

1,526

1 year

rr_ExpenseExampleNoRedemptionYear01

108

3 years

rr_ExpenseExampleNoRedemptionYear03

384

5 years

rr_ExpenseExampleNoRedemptionYear05

681

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,526

Columbia Acorn International Select | Class Inst2

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.31%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.20%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.23%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.97%

1 year

rr_ExpenseExampleYear01

$ 99

3 years

rr_ExpenseExampleYear03

358

5 years

rr_ExpenseExampleYear05

638

10 years

rr_ExpenseExampleYear10

1,434

1 year

rr_ExpenseExampleNoRedemptionYear01

99

3 years

rr_ExpenseExampleNoRedemptionYear03

358

5 years

rr_ExpenseExampleNoRedemptionYear05

638

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,434

Columbia Acorn International Select | Class Inst3

Risk/Return:

rr_RiskReturnAbstract

Management fees

rr_ManagementFeesOverAssets

0.89%

Distribution and/or service (12b-1) fees

rr_DistributionAndService12b1FeesOverAssets

none

Other expenses

rr_OtherExpensesOverAssets

0.26%

^[1]

Total annual Fund operating expenses

rr_ExpensesOverAssets

1.15%

^[2]

Fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.23%)

^[3]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_NetExpensesOverAssets

0.92%

1 year

rr_ExpenseExampleYear01

$ 94

3 years

rr_ExpenseExampleYear03

343

5 years

rr_ExpenseExampleYear05

611

10 years

rr_ExpenseExampleYear10

1,377

1 year

rr_ExpenseExampleNoRedemptionYear01

94

3 years

rr_ExpenseExampleNoRedemptionYear03

343

5 years

rr_ExpenseExampleNoRedemptionYear05

611

10 years

rr_ExpenseExampleNoRedemptionYear10

$ 1,377

[1] Other expenses have been restated to reflect current transfer agency fees paid by the Fund.

[2] “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses.

[3] Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through June 30, 2020, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.31% for Class A shares, 1.06% for Class Adv shares, 2.06% for Class C shares, 1.06% for Class Inst shares, 0.97% for Class Inst2 shares and 0.92% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through June 30, 2020, such that the Fund’s transfer agency fees do not exceed the annual rates of 0.05% of the average daily net assets of Class Inst2 shares and 0.00% of the average daily net assets of Class Inst3 shares.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	COLUMBIA ACORN TRUST
Prospectus Date	rr_ProspectusDate	May 01, 2019
Document Creation Date	dei_DocumentCreationDate	Jun. 28, 2019