The status as an opponent cannot be freely transferred (G 2/04, OJ 2005, 549). The opponent does not have a right of disposition over his status as a party. If he has met the requirements for an admissible opposition, he is an opponent and remains such until the end of the proceedings or his involvement in them. He cannot offload his status onto a third party (G 3/97, OJ 1999, 245, T 298/97, OJ 2002, 83).

However, in the following two circumstances the status as an opponent may be transferred:

- in the case of universal succession of the opponent (G 4/88, OJ 1989, 480, T 475/88, T 1091/02 date: 2004-07-23, OJ 2005,14); or

- when a relevant part of the opponent's business has been transferred (G 2/04, T 670/95). The transfer or assignment of the opposition to a third party has to be made as part of the transfer or assignment of the opponent's business assets together with the assets in the interests of which the opposition was filed (G 4/88, OJ 1989, 480).

Opponent status may also be transferred in opposition appeal proceedings (T 659/92, OJ 1995, 519, T 670/95, T 19/97). In T 563/89 the board held that the right to lodge an appeal may also be transferred to a third party, based on the same reasons as developed in case G 4/88.

A transfer of an opposition has to be requested at the EPO together with supporting evidence before it can take effect (T 1137/97, T 19/97, T 1911/09). This does not apply to cases of universal succession where the opponent status is automatically acquired from the date of the effective succession (T 6/05, T 425/05, T 2382/10); in the case of universal succession the change may – upon request and production of evidence by either party – be recorded with retroactive effect as from the effective date of the legal succession (T 2357/12).

The EPO has a duty to examine, ex officio, the status of the opponent at all stages of the proceedings. This duty not only extends to the admissibility of the original opposition, but also to the validity of any purported transfer of the status of opponent as a new party (T 1178/04, OJ 2008, 80). Even if the objection of the admisiblity of the appeal and the appellant's status as party is raised very late, namely at the beginning of the oral proceedings before the board, this issue has to be examined ex officio at every stage of the appeal proceedings; an appellant's objection against the late introduction of this issue can therefore not succeed (T 1415/16).