3.2. In appeal proceedings

In G 3/04 the Enlarged Board ruled that an intervener, if the appeal is filed by someone other than them, is a party as of right according to Art. 107, second sentence, EPC. If the intervention is filed during the appeal proceedings, the intervener, again because they can only acquire the status of an opponent, has the same rights and obligations – apart from the right to raise new grounds of opposition – as any opponent who has not filed an appeal. If in this case the sole, or each, appeal has been withdrawn, the appeal proceedings are terminated in respect of all the substantive issues, including the new grounds for opposition raised by the intervener, for all the parties (see also T 694/01, OJ 2003, 250; T 1108/02, T 439/17).

In T 1286/23 of 11 November 2024 date: 2024-11-11 (OJ 2025, A38) the board considered deviating from G 3/04. It argued that the conclusion of the Enlarged Board that "the valid intervener only acquires the status of an opponent" contradicts Art. 107, second sentence, EPC, at least as long as "status of an opponent" is read as "status of an opponent who had been party to the proceedings leading to the appealed decision (but is not itself an appellant within the meaning of Art. 107, first sentence, EPC)". According to the board, for the legislative intent to be respected, procedural conditions that intend to put limitations on the party status in Art. 107 EPC could not apply to interveners. Therefore, it referred the following question to the Enlarged Board: "After withdrawal of all appeals, may the proceedings be continued with a third party who intervened during the appeal proceedings? In particular, may the third party acquire an appellant status corresponding to the status of a person entitled to appeal within the meaning of the Art. 107, first sentence, EPC?".

Following this referral, in G 2/24, the Enlarged Board concluded that the findings of G 3/04 continued to apply and held that the intervener in appeal proceedings does not acquire an appellant status corresponding to the status of a person entitled to appeal within the meaning of Art. 107, first sentence, EPC. Accordingly, the appeal proceedings cannot be continued by the intervener after the withdrawal of all appeals. It reaffirmed that an intervener at appeal becomes a party as of right and the intervention needs to fit into the legal and procedural framework of the boards of appeal as the first and final judicial instance in proceedings under the EPC. The principle of party disposition and the binding nature of the parties' requests limit the procedural actions of all parties in appeal, including interveners. Parties to appeal proceedings as of right do not have a legal status independent of the appeal and conferring such status would require an explicit legal provision in the EPC. Therefore, if the sole or all appeals are withdrawn, the proceedings end in respect to all substantive issues for all parties involved and cannot be continued with an intervener at the appeal stage or any other non-appealing party.

In T 417/22 of 14 January 2026 the proceedings before the board arose from the appeals of the patent proprietor and the original opponent (opponent 1) against the Opposition Division's decision to maintain the patent in amended form. An intervention was subsequently filed. Opponent 1 and the patent proprietor later withdrew their appeals. The intervener requested that the proceedings be stayed in view of the then pending G 1/24. In its interlocutory decision T 417/22 of 7 July 2025, the board agreed to stay the proceedings (see also chapter V.B.2.5.4). Upon resumption of the proceedings following G 2/24, it was undisputed that the case hinged on the admissibility of the intervener's appeal, which had been filed simultaneously with their intervention and only during the already pending appeal proceedings. The Enlarged Board's decision provided a definitive answer that the intervener's appeal had to be considered inadmissible. It was therefore established that the substantive appeal proceedings had terminated without a decision on the merits, on the date of withdrawal of the last admissible appeal.

In G 1/94 (see in this chapter III.P.2.4.2), the Enlarged Board also examined the question of whether an intervener during appeal proceedings could raise any of the grounds for opposition under Art. 100 EPC 1973 (now Art. 100 EPC) even if they had not yet been examined by the opposition division and found in the affirmative. If a fresh ground for opposition was raised, the case should be remitted to the department of first instance unless the patent proprietor wished the board to rule on it there and then. In T 694/01 (OJ 2003, 250), it was made clear that where a board has decided to maintain a patent on the basis of a given set of claims and a description to be added to them, in subsequent appeal proceedings confined to the issue of the adaptation of the description the previous decision is res judicata and the intervener cannot therefore challenge this decision by introducing a new ground of opposition.