The right of priority established in the Paris Convention for the Protection of Industrial Property allows a patent applicant to claim the filing date of a first application for any subsequent applications for the same invention filed within twelve months in another Paris Convention Contracting State. This right may be claimed by the person who has filed an application or their successor in title. If priority is not validly claimed, patent applications and patents relying on the right may be rejected, revoked or invalidated. National and regional rules governing who may claim priority, whether a priority right may be divided or shared, whether it may be transferred independently of the priority application and the rights to the invention, and the requirements for a valid transfer differ from country to country. The issue of whether priority has been validly claimed may therefore depend on which country’s law applies, which depends on the characterisation of the issues. The aim of this article is to provide a European perspective on the law applicable to the right of priority.