In its decision G 2/24, the Enlarged Board of Appeal (EBoA) of the European Patent Office (EPO) confirmed the procedural boundaries for third-party intervention during appeal proceedings. The decision upholds the precedent set in G 3/04, confirming that a third party who intervenes at the appeal stage does not acquire the status of an appellant and cannot continue the appeal proceedings if all original appellants withdraw.
Background
Within nine months of the grant of a European patent, any person may challenge the patent by filing an opposition at the EPO (Article 99 EPC). Any party that does so becomes a party to the opposition proceedings before the Opposition Division.
If the Opposition Division issues any decision that adversely affects a party to the opposition proceedings (which could be one the opponent(s), the patent proprietor, or both), the affected party may file an appeal within two months of the decision. They then become an “appellant” and a party to the appeal proceedings before the Board of Appeal (Article 107 EPC).
During the opposition proceedings, an “assumed infringer” may intervene in the opposition. An assumed infringer is a third party against whom the opposed patent has been asserted, or who has instituted proceedings for a ruling of non-infringement of the opposed patent. Interveners to opposition proceedings become a party to the opposition proceedings with the same rights as if they had filed an opposition within nine months of patent grant. This includes the right to appeal any adverse decision issued by the Opposition Division (Article 105 EPC).
In the event an assumed infringer emerges after the opposition stage has concluded, previous decisions G 1/94 and G 3/04 of the EBoA held that they may intervene in any subsequent appeal. However, they would not have the status of an appellant, since they were not a party to the opposition procedure. Instead, they would assume the status of a “party to the appeal proceedings as of right” (Article 107 EPC). In the event that all appellants withdraw from the appeal, the appeal proceedings would terminate, regardless of whether any “parties to the appeal proceedings as of right” remained.
The referring Board of Appeal (BoA) in T 1286/23 challenged this precedent, arguing that the logic of G 3/04 was unconvincing and potentially inconsistent with the broader legal framework of the EPC. It questioned whether an intervener could acquire appellant status and continue proceedings independently.
The Decision
The EBoA held that:
- Interveners at the appeal stage are participants to the appeal initiated by adversely affected parties.
- They do not acquire appellant status under Article 107 EPC.
- If all appellants withdraw, the proceedings must terminate, even if an appeal intervener remains.
The decision reaffirms the conclusions of the previous EBoA decision G 3/04 on the matter, rejecting the BoA challenge. To arrive at this decision, the EBoA found no substantive changes to Articles 99, 105, or 107 EPC since G 3/04 that would warrant a different interpretation. It reiterated that Article 107 EPC guarantees participation rights for parties as of right but does not confer appellant status.
The EBoA also undertook a comparative analysis of intervention practices across EPC member states, none of which supported a departure from G 3/04. Finally, the EBoA cautioned against referrals from Boards of Appeal based solely on disagreement with earlier EBoA decisions, reinforcing the importance of legal consistency and legislative intent under Article 112 EPC.
Outcomes
G 2/24 changes very little and instead merely confirms previous decisions of the EBoA. There is no doubt now that, whilst third parties may intervene in pending appeals and acquire rights of participation, their rights are less than those of appellants who were parties to the original decision under appeal. Appeal proceedings are driven by the appellant(s) and, if all appellants withdraw, the presence of a “party to the appeal proceedings as of right” is of no consequence. The appeal proceedings must terminate.
Phil Horler
Electronics, Computing & Physics group
This publication is a general summary of the law. It should not replace legal advice tailored to your specific circumstances.
© Withers & Rogers LLP October 2025
