JOINT FILING AGREEMENT

25 of 28

Exhibit 1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(f) of the Securities Exchange Act of 1934, as amended, the undersigned hereby agree to the joint filing on behalf of each of us of an amendment to Schedule 13D relating to the Ordinary Shares of Celanese AG, a German stock corporation, and that any subsequent amendments thereto filed by any of us will be filed on behalf of each of us. This Agreement may be included as an exhibit to such joint filing.

DATE: September 20, 2004
	BCP CRYSTAL ACQUISITION GMBH & CO. KG
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BCP ACQUISITION GMBH & CO. KG
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person
	BCP HOLDINGS GMBH
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person
	BCP MANAGEMENT GMBH
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person
	BCP CAYLUX HOLDINGS LUXEMBOURG S.C.A.
	By:	BCP Caylux Holdings Ltd. 1, its manager
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person
	BCP CAYLUX HOLDINGS LTD. 1
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

26 of 28

	BLACKSTONE CAPITAL PARTNERS (CAYMAN) IV L.P.
	By:	Blackstone Management Associates (Cayman) IV L.P., its general partner

By:   Xxxxxxxxxx XX Associates (Cayman) IV Ltd., its general partner 

	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE CAPITAL PARTNERS (CAYMAN) IV-A L.P.
	By:	Blackstone Management Associates
		(Cayman) IV L.P., its general partner

By:   Xxxxxxxxxx XX Associates (Cayman) IV Ltd., its general partner 

	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE FAMILY INVESTMENT PARTNERSHIP (CAYMAN) IV-A L.P.
	By:	Blackstone Management Associates
		(Cayman) IV L.P., its general partner

By:   Xxxxxxxxxx XX Associates (Cayman) IV Ltd., its general partner 

	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE CHEMICAL COINVEST PARTNERS (CAYMAN) L.P.
	By:	Blackstone Management Associates
		(Cayman) IV L.P., its general partner

	By:	Xxxxxxxxxx XX Associates (Cayman)
		IV Ltd., its general partner

	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE MANAGEMENT ASSOCIATES (CAYMAN) IV L.P.
	By:	Xxxxxxxxxx XX Associates (Cayman) IV Ltd., its general partner

	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

27 of 28

	XXXXXXXXXX XX ASSOCIATES (CAYMAN) IV LTD.
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	XXXXXXXXXX XXXXXXX HOLDINGS CAPITAL PARTNERS (CAYMAN) IV LTD.
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE CAPITAL PARTNERS (CAYMAN) LTD. 1
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

	BLACKSTONE CAPITAL PARTNERS (CAYMAN) LTD. 2
	By:	/s/ Xxxxx Xxx
		Title:	Name: Xxxxx Xxx Authorized Person

	BLACKSTONE CAPITAL PARTNERS (CAYMAN) LTD. 3
	By:	/s/ Xxxxx Xxx
		Title:	Name: Xxxxx Xxx Authorized Person

	BCP CRYSTAL HOLDINGS LTD. 2
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Authorized Person

28 of 28

	CRYSTAL US HOLDINGS 3 L.L.C.
	By:	/s/ Xxxxx Xxx
		Name:	Xxxxx Xxx
		Title:	Manager

/s/ Xxxxx X. Xxxxxxxx  

XXXXX X. XXXXXXXX
 

/s/ Xxxxxxx X. Xxxxxxxxxx  

XXXXXXX X. XXXXXXXXXX