Legal Alert: EPO Enlarged Board of Appeal Raises Bar for Challenging Priority Claims at the EPO 


Challenges to the validity of the “Patent Cooperation Treaty joint applicant” have been a problem for many applicants at the European Patent Office. On October 10, 2023, the EPO’s highest authority, the Enlarged Board of Appeal, issued its decision in the consolidated cases of G 1/22 and G 2/22, confirming the EPO’s competence to assess a party’s entitlement to priority.

Third parties have increasingly challenged the validity of priority claims of European patents during opposition proceedings. Their arguments hinge on the fact that a PCT application is jointly filed in the name of several applicants and the European patent application claiming priority to the PCT application is not jointly filed by the same applicants of the PCT application. This created a situation where, unless clear evidence of a valid transfer of priority rights was available, the Boards of Appeal at the EPO have, in some high-profile instances, revoked patents.

In response to these developments, the Enlarged Board of Appeal was tasked with answering two primary questions. First, the EBoA had to determine whether the European Patent Convention confers jurisdiction on the EPO to determine whether a party validly claims to be a successor in title as referred to in Article 87(1)(b) EPC. Second, if yes, it had to determine whether a party B can validly rely on the priority right claimed in a PCT application for the purpose of claiming priority rights under Article 87(1) EPC under the following conditions:

  1. a PCT application designates party A as applicant for the U.S. only and party B as applicant for other designated states, including regional European patent protection, and
  2. the PCT application claims priority from an earlier patent application that designates party A as the applicant, and
  3. the priority claimed in the PCT application is in compliance with Article 4 of the Paris Convention.

The EBoA has affirmed that the EPO indeed is competent to assess whether a party is entitled to claim priority under Article 87(1) EPC. In particular, the EBoA held that there is a rebuttable presumption under the autonomous law of the EPC that the applicant claiming priority in accordance with Article 88(1) EPC and the corresponding Implementing Regulations is entitled to claim priority. Therefore, priority rights are autonomous rights under the EPC and should be assessed only in the context of the EPC, regardless of any national laws. The creation, existence, and effects of priority rights are governed only by the EPC (and by the Paris Convention through its relationship with the EPC).

The decision confirms that where the European patent application derives from a PCT application jointly filed by several applicants, amongst them the applicant of the priority application, no further proof of a transfer of the priority right to the applicant of the subsequent application is needed. Therefore, the assignment of priority rights does not have to be in writing and/or signed by or on behalf of the parties to the transaction, since this would establish a high threshold in view of the national laws (Reasons 100, 105).

It was also pointed out that this presumption should be rebuttable since in rare exceptional cases the priority applicant may have legitimate reasons not to allow the subsequent applicant to rely on the priority. However, the party challenging the entitlement to priority cannot just raise speculative doubts but must demonstrate that specific facts support serious doubts about the subsequent applicant’s entitlement to priority. Moreover, the presumption of entitlement exists on the date on which the priority is claimed and the rebuttal of the presumption must also relate to this date, as later developments cannot affect the rebuttable presumption (Reasons 108-110).

As good news for patent proprietors and applicants, this decision significantly raises the bar for challenging the validity of a priority claim at the EPO, especially on the grounds that the right to claim priority was not effectively transferred.