SECURITIES AND EXCHANGE COMMISSION	
Washington, D.C. 20549	
 	
SCHEDULE 13G	
 	
Under the Securities Exchange Act of 1934	
(Amendment No. )*	
 	
CASTLIGHT HEALTH, INC.	
(Name of Issuer)	
 	
Class B Common Stock, par value $0.0001 per share	
(Title of Class of Securities)	
 	
14862Q100	
(CUSIP Number)	
 	
April 2, 2014	
(Date of Event Which Requires Filing of This Statement)	

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:	
 	
¨	Rule 13d-1(b)	
x	Rule 13d-1(c)	
¨	Rule 13d-1(d)	
 	
(Page 1 of 11 Pages)	
 
______________________________
*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 the Notes).

 

 	

CUSIP No. 14862Q100	13G	Page  2  of 11 Pages	

1	NAME OF REPORTING PERSON
Adage Capital Partners, L.P.	
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
0	
	6	SHARED VOTING POWER
554,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
554,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
554,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5%	
12	TYPE OF REPORTING PERSON
PN	

 	

CUSIP No. 14862Q100	13G	Page  3  of 11 Pages	

1	NAME OF REPORTING PERSON
Adage Capital Partners GP, L.L.C.	
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
0	
	6	SHARED VOTING POWER
554,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
554,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
554,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5%	
12	TYPE OF REPORTING PERSON
OO	

 

CUSIP No. 14862Q100	13G	Page  4  of 11 Pages	
 
1	NAME OF REPORTING PERSON
Adage Capital Advisors, L.L.C.	
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
0	
	6	SHARED VOTING POWER
554,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
554,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
554,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5%	
12	TYPE OF REPORTING PERSON
OO	

 	

CUSIP No. 14862Q100	13G	Page  5  of 11 Pages	
 
1	NAME OF REPORTING PERSON
Robert Atchinson	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ¨	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
United States	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
554,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
554,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
554,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5%	
12	TYPE OF REPORTING PERSON
IN	

 	

CUSIP No. 14862Q100	13G	Page  6  of 11 Pages	
 
1	NAME OF REPORTING PERSON
Phillip Gross	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP	(a) ¨
(b) ¨	
3	SEC USE ONLY	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
United States	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON WITH:	5	SOLE VOTING POWER
0	
	6	SHARED VOTING POWER
554,000	
	7	SOLE DISPOSITIVE POWER
0	
	8	SHARED DISPOSITIVE POWER
554,000	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
554,000	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
5%	
12	TYPE OF REPORTING PERSON
IN	

 	

CUSIP No. 14862Q100	13G	Page  7  of 11 Pages	

Item 1(a).	NAME OF ISSUER	
 	The name of the issuer is CASTLIGHT HEALTH, INC. (the “Company”).	

Item 1(b).	ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES	
 	The Company’s principal executive offices are located at Two Rincon Center, 121 Spear Street, Suite 300, San Francisco, CA 94105.	

Item 2(a).	NAME OF PERSON FILING	
 	This statement is filed by:	

 	(i)	Adage Capital Partners, L.P., a Delaware limited partnership ("ACP") with respect to the shares of Class B Common Stock directly owned by it;	
 	 	
 	(ii)	Adage Capital Partners GP, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACPGP"), as general partner of ACP with respect to the shares of Class B Common Stock directly owned by ACP;	
 	 	
 	(iii)	Adage Capital Advisors, L.L.C., a limited liability company organized under the laws of the State of Delaware ("ACA"), as managing member of ACPGP, general partner of ACP, with respect to the shares of Class B Common Stock directly owned by ACP;	
 	 	
 	(iv)	Robert Atchinson ("Mr. Atchinson"), as managing member of ACA, managing member of ACPGP, general partner of ACP with respect to the shares of Class B Common Stock directly owned by ACP; and	
 	 	
 	(v)	Phillip Gross ("Mr. Gross"), as managing member of ACA, managing member of ACPGP, general partner of ACP with respect to the shares of Class B Common Stock directly owned by ACP.	
 	 	
 	The foregoing persons are hereinafter sometimes collectively referred to as the “Reporting Persons.”  Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party.	
 
Item 2(b).	ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE	
 	The address of the business office of each of the Reporting Persons is 200 Clarendon Street, 52nd floor, Boston, Massachusetts 02116.	

 

CUSIP No. 14862Q100	13G	Page  8  of 11 Pages	

Item 2(c).	CITIZENSHIP	
 	ACP is a limited partnership organized under the laws of the State of Delaware.  ACPGP and ACA are limited liability companies organized under the laws of the State of Delaware.  Messrs. Gross and Atchinson are citizens of the United States.	

Item 2(d).	TITLE OF CLASS OF SECURITIES	
 	Class B Common Stock, par value $0.0001 per share (the "Class B Common Stock").	

Item 2(e).	CUSIP NUMBER	
 	14862Q100	

Item 3.	IF THIS STATEMENT IS FILED PURSUANT TO Rules 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;	
 	(b)	¨	Bank as defined in Section 3(a)(6) of the Act;	
 	(c)	¨	Insurance company as defined in Section 3(a)(19) of the Act;	
 	(d)	¨	Investment company registered under Section 8 of the Investment Company Act of 1940;	
 	(e)	¨	An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);	
 	(f)	¨	An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);	
 	(g)	¨	A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);	
 	(h)	¨	A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act;	
 	(i)	¨	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act;	
 	(j)	¨	A non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J);	
 	(k)	¨	Group, in accordance with Rule 13d-1(b)(1)(ii)(K).	
 
 	If filing as a non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J), please
specify the type of institution: Not applicable.                                       	

 

CUSIP No. 14862Q100	13G	Page  9  of 11 Pages	

Item 4.	OWNERSHIP	

 	A.	Adage Capital Partners, L.P., Adage Capital Partners GP, L.L.C. and Adage Capital Advisors , L.L.C.	
 	 	 	(a)	Amount beneficially owned:  554,000	
 	 	 	(b)	Percent of class: 5%.  The percentages used herein and in the rest of Item 4 are calculated based upon 11,100,000 shares of Class B Common Stock outstanding as of December 31, 2013 as reported in the Company’s Form S-1/A dated March 11, 2014.	
 	 	 	(c)	(i)	Sole power to vote or direct the vote:  0	
 	 	 	 	(ii)	Shared power to vote or direct the vote: 554,000	
 	 	 	 	(iii)	Sole power to dispose or direct the disposition:  0	
 	 	 	 	(iv)	Shared power to dispose or direct the disposition of:  554,000	

ACP has the power to dispose of and the power to vote the shares of Class B Common Stock beneficially owned by it, which power may be exercised by its general partner, ACPGP.  ACA, as managing member of ACPGP, directs ACPGP's operations. Neither ACPGP nor ACA directly own any shares of Class B Common Stock.  By reason of the provisions of Rule 13d-3 of the Securities Exchange Act of 1934 (the "Act"), ACPGP and ACA may be deemed to beneficially own the shares owned by ACP.	
  
 	B.	Robert Atchinson and Phillip Gross	
 	 	 	(a)	Amount beneficially owned:  554,000	
 	 	 	(b)	Percent of class:  5%	
 	 	 	(c)	(i)	Sole power to vote or direct the vote:  0	
 	 	 	 	(ii)	Shared power to vote or direct the vote:  554,000	
 	 	 	 	(iii)	Sole power to dispose or direct the disposition:  0	
 	 	 	 	(iv)	Shared power to dispose or direct the disposition:  554,000	
 
Messrs. Atchinson and Gross, as managing members of ACA, have shared power to vote the Class B Common Stock beneficially owned by ACP.  Neither Mr. Atchinson nor Mr. Gross directly own any shares of Class B Common Stock.  By reason of the provisions of Rule 13d-3 of the Act, each may be deemed to beneficially own the shares beneficially owned by ACP.	
 
Item 5.	OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS	
 	Not applicable.	

 

CUSIP No. 14862Q100	13G	Page  10  of 11 Pages	

Item 6.	OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON	
 	Not applicable.	

Item 7.	IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY OR CONTROL PERSON	
 	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	
 
 	Each of the Reporting Persons hereby makes the following certification:	
 	 	
 	By signing below each Reporting Person certifies that, to the best of his or its knowledge and belief, the securities referred to above 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. 14862Q100	13G	Page  11  of 11 Pages	
SIGNATURES
After reasonable inquiry and to the best of his or its knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.
DATE: April 11, 2014

 	 	 	
ADAGE CAPITAL PARTNERS, L.P.	 	
By:  Adage Capital Partners GP, L.L.C.,	 	
its general partner	 	
 	 	
By:  Adage Capital Advisors, L.L.C.,	 	
its managing member	 	
 	 	
/s/ Robert Atchinson	 	
Name:  Robert Atchinson	 	
Title: Managing Member	 	

 
ADAGE CAPITAL PARTNERS GP, L.L.C.	
By:  Adage Capital Advisors, L.L.C.,	
its managing member	
 	
/s/ Robert Atchinson	
Name:  Robert Atchinson	
Title: Managing Member	

ADAGE CAPITAL ADVISORS, L.L.C.	
 	
/s/ Robert Atchinson	
Name:  Robert Atchinson	
Title: Managing Member	

/s/ Robert Atchinson	
ROBERT ATCHINSON, individually	

/s/ Phillip Gross	
PHILLIP GROSS, individually	

 	

CUSIP No. 14862Q100	13G	Page  12  of 11 Pages	
EXHIBIT 1
JOINT FILING AGREEMENT
PURSUANT TO RULE 13d-1(k)
The undersigned acknowledge and agree that the foregoing statement on Schedule 13G is filed on behalf of each of the undersigned and that all subsequent amendments to this statement on Schedule 13G shall be filed on behalf of each of the undersigned without the necessity of filing additional joint filing agreements. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning him or it contained herein and therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that he or it knows or has reason to believe that such information is inaccurate.
 
DATE: April 11, 2014
 
ADAGE CAPITAL PARTNERS, L.P.	
By:  Adage Capital Partners GP, L.L.C.,	
its general partner	
 	
By:  Adage Capital Advisors, L.L.C.,	
its managing member	
 	
/s/ Robert Atchinson	
Name:  Robert Atchinson	
Title: Managing Member	

ADAGE CAPITAL PARTNERS GP, L.L.C.	
By:  Adage Capital Advisors, L.L.C.,	
its managing member	
 	
/s/ Robert Atchinson	
Name:  Robert Atchinson	
Title: Managing Member	

ADAGE CAPITAL ADVISORS, L.L.C.	
 	
/s/ Robert Atchinson	
Name:  Robert Atchinson	
Title: Managing Member	

/s/ Robert Atchinson	
ROBERT ATCHINSON, individually	

/s/ Phillip Gross	
PHILLIP GROSS, individually