Supplement dated June 27, 2016

to the Prospectus and Summary Prospectus of the following Fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Thermostat FundSM	5/1/2016

1. The table under the caption “Fees and Expenses of the Fund” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:

Shareholder Fees (fees paid directly from your investment)
	Class A	Class C	Classes R4, R5, Y and Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75%	None	None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00% (a)	1.00% (b)	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class C	Class R4	Class R5	Class Y	Class Z
Management fees	0.10%	0.10%	0.10%	0.10%	0.10%	0.10%
Distribution and/or service (12b-1) fees	0.25%	1.00%	0.00%	0.00%	0.00%	0.00%
Other expenses(c)	0.17%	0.17%	0.17%	0.15%	0.10%	0.17%
Acquired fund fees and expenses	0.52%	0.52%	0.52%	0.52%	0.52%	0.52%
Total annual Fund operating expenses(d)	1.04%	1.79%	0.79%	0.77%	0.72%	0.79%
Fee waivers and/or expense reimbursements(e)	(0.02%)	(0.02%)	(0.02%)	(0.01%)	(0.01%)	(0.02%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.02%	1.77%	0.77%	0.76%	0.71%	0.77%

(a)	This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions.
(b)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(c)	Other expenses have been restated and are based on estimated amounts for the Fund's current fiscal year, taking into consideration changes in the method of allocating transfer agent expenses among Class A, Class C, Class R4 and Class Z shares of the Fund.
(d)	“Total annual Fund operating expenses” include acquired fund (Portfolio Fund) fees and expenses (expenses the Fund incurs indirectly through its investments in other funds) and may be higher than “Total Net Expenses” shown in the Financial Highlights section of this prospectus because “Total Net Expenses” do not include Portfolio Fund (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 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 the Portfolio Funds (acquired funds)), do not exceed the annual rates of 0.50% for Class A shares, 1.25% for Class C shares, 0.25% for Class R4 shares, 0.24% for Class R5 shares, 0.19% for Class Y shares and 0.25% for Class Z shares, through April 30, 2017. This arrangement may only be modified or amended with approval from the Fund and the Investment Manager.
2.	The expense example table that appears under the caption “Fees and Expenses of the Fund – Example” in the “Summary of the Fund” section of the Prospectus and the Summary Prospectus is hereby superseded and replaced with the following:

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$673	$885	$1,114	$1,771
Class C (assuming redemption of all shares at the end of the period)	$280	$561	$ 968	$2,104
Class C (assuming no redemption of shares)	$180	$561	$ 968	$2,104
Class R4 (whether or not shares are redeemed)	$ 79	$250	$ 437	$ 976
Class R5 (whether or not shares are redeemed)	$ 78	$245	$ 427	$ 953
Class Y (whether or not shares are redeemed)	$ 73	$229	$ 400	$ 894
Class Z (whether or not shares are redeemed)	$ 79	$250	$ 437	$ 976

Shareholders should retain this Supplement for future reference.

SUP235_12_001_(06/16)