Even though the right of priority is a mainstay of the Paris Convention, the European Patent Convention (EPC) provides complete, self-contained requirements for a valid claim to priority. Inter alia, the first application whose priority is claimed must have been filed by the applicant of the European application (or International (PCT) application designating the European regional phase) or his predecessor in title. In short, the applicant must be entitled to claim priority at the time of filing the European or International application.

The first-inventor-to-file provision of AIA changed who is entitled to be an applicant in US national applications, requiring US representatives to remain vigilant to possible changes in applicants between a European or International application and a US national application whose priority is claimed. A lapse in vigilance can manifest as an irreparable invalidation of the right to priority, which cannot be restored even if the applicant subsequently acquires title to the invention.

Like in the US, the entitlement to grant of a patent can be settled at any time during the grant procedure, or even after grant, by appropriate assignment. However, if a change in applicant has occurred, or if the chain of title between successive applicants is not clear, a formal assignment of the priority right must implicitly and tacitly take place before the filing date of the European or International application. The EPC does not stipulate the formal requirements for an assignment of priority rights to become effective vis-à-vis the EPO, but the assignment is subject to the law applicable to national applications in each of the EPC Contracting State. The case law has established that an assignment of rights in and to a European application should preferably:

  • be made in writing and require the signature of the parties to the contract (signed at least by the assignor, but preferably by all parties);
  • be dated and executed before the filing date of the European or International application (preferably witnessed or notarised);
  • explicitly specify details of the first application whose priority is claimed, and expressly assign the corresponding priority right; and
  • immediately assign the corresponding priority right (not just agree to assign), and have the corresponding priority right accepted by the assignee.

If the assignment of the priority right cannot be effected before the filing date of the European or International application, or if the chain of title between successive applicants is not clear, the European or International application should be filed in the name of all of the applicant(s) who filed the first application whose priority is claimed. The European or International application can be transferred at a later time.

In most cases, invalidation of the right to priority will only pose difficulties in the presence of a disclosure published between the claimed priority date and the filing date of the European or International application. However, we think that such difficulties can be circumvented by taking these suggested measures to ensure a clear chain of title between successive applicants.