UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
Under the Securities Exchange Act of 1934
TRINSEO SA
(Name of Issuer)
Common Stock
(Title of Class of Securities)
L9340P101
(CUSIP Number)
December 31, 2017
(Date of Event which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
[X] Rule 13d-1(b)
[   ] Rule 13d-1(c)
[   ] Rule 13d-1(d)
* The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see Instructions).
CUSIP No.: L9340P101

1	NAME OF REPORTING PERSON
Boston Partners
I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)
98-0202744	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) [   ]
(b) [   ]	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER
1,545,349	
	6	SHARED VOTING POWER
3,534	
	7	SOLE DISPOSITIVE POWER
2,337,032	
	8	SHARED DISPOSITIVE POWER
0	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
2,337,032	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
[   ]	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5.35%	
12	TYPE OF REPORTING PERSON
IA	
CUSIP No.: L9340P101

ITEM 1(a).	NAME OF ISSUER:
TRINSEO SA	
ITEM 1(b).	ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:
1000 Chesterbrook Boulevard Suite 300
Berwyn, PA 19312	
ITEM 2(a).	NAME OF PERSON FILING:
Boston Partners	
ITEM 2(b).	ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE:
One Beacon Street
30th Floor
Boston, MA 02108	
ITEM 2(c).	CITIZENSHIP:
Delaware	
ITEM 2(d).	TITLE OF CLASS OF SECURITIES:
Common Stock	
ITEM 2(e).	CUSIP NUMBER:
L9340P101	
ITEM 3.	IF THIS STATEMENT IS FILED PURSUANT TO SECTION 240.13d-1(b), or 13d-2(b) or (c) CHECK WHETHER THE PERSON FILING IS A:	
	(a)
[ ]	Broker or dealer registered under Section 15 of the Act (15 U.S.C. 78c);	
	(b)
[ ]	Bank as defined in Section 3(a)(6) of the Act (15 U.S.C. 78c);	
	(c)
[ ]	Insurance company as defined in Section 3(a)(19) of the Act (15 U.S.C. 78c);	
	(d)
[ ]	Investment company registered under Section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8);	
	(e)
[X]	An investment adviser in accordance with 240.13d-1(b)(1)(ii)(E);	
	(f)
[ ]	An employee benefit plan or endowment fund in accordance with 240.13d-1(b)(1)(ii)(F);	
	(g)
[ ]	A parent holding company or control person in accordance with 240.13d-1(b)(1)(ii)(G);	
	(h)
[ ]	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);	
	(i)
[ ]	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);	
	(j)
[ ]	A non-U.S. institution in accordance with 240.13d-1(b)(1)(ii)(J);	
	(k)
[ ]	Group, in accordance with 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with 240.13d1(b)(1)(ii)(J), please specify the type of institution:	
		
ITEM 4.	OWNERSHIP	
	(a) Amount beneficially owned:	
	2,337,032	
	(b) Percent of class:	
	5.35%	
	(c) Number of shares as to which the person has:	
	(i) sole power to vote or to direct the vote:	
	1,545,349	
	(ii) shared power to vote or to direct the vote:	
	3,534	
	(iii) sole power to dispose or direct the disposition of:	
	2,337,032	
	(iv) shared power to dispose or to direct the disposition of:	
	0	
ITEM 5.	OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS:
If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [ ].	
ITEM 6.	OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON:
This Schedule is being filed with respect to 2,337,032 shares Trinseo Sa
(the Common Stock) held by Boston Partners on 12/31/2017 for the
discretionary account of certain clients. By reason of rule 13d-3 under the act
Boston Partners may be deemed to be a beneficial owner of such Common
Stock. To the knowledge of Boston Partners no person has the right to receive
or the power to direct the receipt of dividends from or the proceeds from the
sale of such Common Stock which represents more than 5% of the
outstanding shares of the Common Stock referred to in item 4(b) hereof.	
ITEM 7.	IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY:
Not applicable.	
ITEM 8.	IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP:
Not applicable.	
ITEM 9.	NOTICE OF DISSOLUTION OF GROUP:
Not applicable.	
ITEM 10.	CERTIFICATION:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.	
CUSIP No.: L9340P101
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

February 13 2018	Boston Partners
By:
/s/ LIANA SAFANOV
Name:
LIANA SAFANOV
Title:
Senior Compliance Manager	
Attention — Intentional misstatements or omissions of fact constitute Federal criminal violations (See 18 U.S.C. 1001).