Relief for US applicants - EPO takes a pragmatic decision on priority

The EPO’s Enlarged Board of Appeal has issued a decision favouring patent applicants on the often tricky question of priority. This may come as a relief to US-based applicants, particularly with pre-AIA priority applications.


We previously reported that the EPO’s Boards of Appeal had requested clarification of matters relating to priority. The issue has implications for many applications, particularly PCT applications with pre-AIA priority applications.

The issue arose during an opposition against Alexion Pharmaceuticals’ patent EP1755674, and the Board of Appeal referred the following questions of law to the Enlarged Board of Appeal:

  1. Does the EPC confer 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?
  2. If yes to Q1, can a party B validly rely on the priority right claimed in a PCT-application for the purpose of claiming priority rights under Article 87(1) EPC in a case where:
    1. a PCT-application designates party A as applicant for the US 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 an applicant and
    3. the priority claimed in the PCT-application is in compliance with Article 4 of the Paris Convention?

The Enlarged Board of Appeal had preliminarily hinted that it was inclined to answer the second question in the affirmative, thereby supporting the so-called PCT joint applicants approach. However, it had refrained from expressing an opinion on the broader-reaching first question, given the split of opinions among the parties and in the numerous amicus curiae briefs.


In a dense 59-page decision, the Enlarged Board of Appeal has answered both questions in the affirmative.

Firstly, the Enlarged Board deems the EPO competent to determine entitlement to priority under the autonomous law of the European Patent Convention (EPC).

The Enlarged Board drew a distinction between the entitlement to file an application (i.e. ownership), which Article 60(3) EPC and the Protocol on Recognition confirm is the jurisdiction of national courts, and the determination of priority entitlement. For the latter, the Enlarged Board reasoned that it was already accepted practice for the EPO to determine the “where”, “what” and “when” requirements of priority, and so the additional determination of the “who” requirement would allow the EPO to comprehensively assess the patentability of an invention.

Secondly, the Enlarged Board concluded that there should be a rebuttable presumption that an applicant claiming priority is entitled to claim priority even where the priority applicant is not identical with the subsequent applicant(s). Their rationale is that consent or cooperation of the priority applicant is usually required to meet the formal requirements of making a declaration of priority, thus the act of joint filing implies an agreement between the parties. This rebuttable presumption applies irrespective of whether the subsequent European application stems from a PCT application, or “whether and to which extent the members of a plurality of co-applicants for the priority application overlap with the group of co-applicants for the subsequent application” (Reason 107).

Applying this principle to the second referred question, the Enlarged Board of Appeal answered in the affirmative. The Enlarged Board also confirmed that the new presumption of validity around priority entitlement is a “strong” presumption under normal circumstances, thus the hurdle for rebuttal is higher and requires any challenger to demonstrate “serious doubts” about priority entitlement (Reason 110).

The Enlarged Board stepped back from formally endorsing the validity of the PCT joint applicants approach, however, and it confirmed that implied agreements can be challenged before the EPO, for example where it can be shown that one party acted in bad faith or that a relevant dispute exists between the parties.

The Enlarged Board of Appeal was also careful to clarify that “an agreement cannot be implied if not all of a plurality of priority applicants are applicants or co-applicants for the subsequent application” (Reason 137), thereby ensuring that this decision does not conflict with the high-profile case in 2020 in which an EPO Board of Appeal dismissed the Broad Institute’s appeal against the revocation of a key patent relating to the CRISPR-Cas genome editing technology.


The Enlarged Board of Appeal’s decision is good news for applicants and patentees across the board, as the EPO is adopting a more permissive view of priority entitlement.

By endorsing the concept of an implied agreement within the filing of PCT applications, the Enlarged Board has accepted historic US practices around priority, which should come as a relief for applicants and patentees with pre-AIA US priority applications.

More generally, in establishing a rebuttable presumption of priority entitlement, the Enlarged Board of Appeal has shifted the burden of invalidating a priority claim on formal grounds on to third parties. This represents a significant shift in practice before the EPO, in which attacks on formal aspects of entitlement to priority are a routine part of opposition proceedings, with the burden of proof usually being on patentees to demonstrate the appropriate transfer of priority rights. The new presumption of validity around priority entitlement means that such attacks are now less likely to succeed given the requirement for the challenger to demonstrate “serious doubts”, and the inherent difficulty for such parties to demonstrate the absence of a transfer of rights from the priority applicant to the subsequent applicant.


The Enlarged Board of Appeal has delivered a landmark decision on formal priority entitlement at the EPO.
The decision accepts historic US practices around priority, which should come as a relief for applicants and patentees with pre-AIA US priority applications.
The decision establishes a rebuttable presumption of priority entitlement, shifting the burden of demonstrating an invalid priority claim to third parties.