Exhibit 99.4

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), the undersigned hereby agree to (i) the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the American Depositary Shares of 21Vianet Group, Inc. and (ii) that this Joint Filing Agreement be included as an exhibit to such joint filing, provided that, as contemplated by Section 13d-1(k)(ii) of the Exchange Act, no person shall be responsible for the completeness and accuracy of the information concerning the other persons making the filing unless such person knows or has reason to believe such information is inaccurate.

This Joint Filing Agreement may be executed in any number of counterparts all of which together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned hereby execute this Agreement as of this 25th  day of October, 2013.

ESTA INVESTMENTS PTE. LTD.
By:	/s/ Rohit Sipahimalani
	Name:	Rohit Sipahimalani
	Title:	Authorised Signatory

TEMBUSU CAPITAL PTE. LTD.
By:	/s/ Chia Yue Joo
	Name:	Chia Yue Joo
	Title:	Director

TEMASEK HOLDINGS (PRIVATE) LIMITED
By:	/s/ Rohit Sipahimalani
	Name:	Rohit Sipahimalani
	Title:	Authorised Signatory