4. Against whom to bring an action for invalidation of an impeding patent?

The natural defendant to the validity of a patent is the patentee himself, in his capacity as holder of the exclusive right being contested.

However, in the case of a request for cancellation as a defense to an infringement action, the adversary is not necessarily the patent owner: it may also be the exclusive licensee or the beneficiary of a compulsory license or ex officio license (see Infringement: taking action [FIC 1639] ).

In this case, it is always possible to file an action for annulment to avoid infringement, but the patent owner must...