Under Art. 107, second sentence, EPC the parties to proceedings before the department of first instance are also parties to the ensuing appeal proceedings, even if they have not personally filed an appeal. Pursuant to Art. 99(3) EPC, opponents as well as the patentee are parties to opposition proceedings. In addition, Art. 105 EPC makes provision for intervention by the assumed infringer. For further details, see chapter III.P. "Intervention".

In T 811/90 (OJ 1993, 728) opposition proceedings had been concluded and the time limit for lodging an appeal had expired. Only the patent proprietor lodged an appeal, but against a separate decision on a point incidental to the opposition. It was held that the other party had no right to be a party to the appeal as he had not been a party to the relevant decision.

However, in a decision concerning an appeal against a Legal Division decision refusing to suspend grant proceedings under R. 13 EPC 1973, the applicant was to be treated as a party to the proceedings. The request for suspension could not be separated from the grant proceedings. The applicant's legal position was directly affected by suspension, because for its duration he was denied the rights under Art. 64(1) EPC 1973 (J 33/95 of 18 December 1995 date: 1995-12-18).

An applicant who was not heard when grant proceedings were suspended at a third party's request pursuant to R. 13 EPC 1973 could still challenge the justification for that suspension. He was a party as of right to any appeal proceedings initiated by the third party against rejection of the latter's request by the EPO (J 28/94 date: 1996-12-04, OJ 1997, 400).

In T 643/91 the appeal of opponent 1 was rejected as inadmissible. Opponent 2 filed an admissible appeal. Opponent 1 was considered by the board to be "any other party to the proceedings" under Art. 107 EPC 1973 and, as a consequence, to be a party as of right in the appeal proceedings of opponent 2. However, in T 898/91 it was held that an opponent whose opposition has been rejected as inadmissible by the opposition division and who has not filed an appeal against this decision is not entitled to be a party to any appeal by the patent proprietor, because he ceases to be a party to the opposition proceedings once the decision on the admissibility of its opposition takes full legal effect.

T 540/13 followed T 1178/04 (OJ 2008, 80) rather than T 898/91, which took another view. The board stated that when an opposition division decides that an opposition is inadmissible in a case where at least one other admissible opposition has been filed, it is not necessary for the opponent of the opposition held inadmissible to appeal this decision in order to preserve its party status in appeal proceedings initiated by another party.

Where two opponents lodge appeals contesting different sets of claims and one subsequently withdraws its appeal, it becomes a party as of right under Art. 107 EPC and the other opponent becomes the sole appellant (see e.g. T 233/93).

Where a company is dissolved and thus ceases to be a legal person, it loses its capacity to be a party to any proceedings. If it was the original appellant, the appeal consequently lapses (T 353/95 and T 2334/08). However, a party's opponent or appellant status does not lapse merely as a result of bankruptcy proceedings being issued (T 696/02).

Third parties commenting under Art. 115 EPC 1973 on the patentability of the invention claimed are not parties to the proceedings before the EPO. See also chapter III.N. "Observations by third parties".