More than nine months have passed since the publication of the patent, which is to be contested and no opposition proceedings are pending, can be according to § 81 Abs. 2 PatG file an invalidity action at the Federal Patent Court. There is a filing fee for this; additional costs may arise. Any patent can be the subject of the lawsuit, which is to be declared null and void on German territory.

For example, lack of patentability can be cited as a ground for invalidity, for example in relation to technical features, which have already been disclosed in another patent specification.

There may be grounds for invalidity:

• lack of patentability
• lack of feasibility
• an inadmissible extension of the patent subject matter compared to the version of the application
• unlawful removal of the invention (only the injured party can claim)
• Expansion of the scope of protection of the patent

A decision on the lawsuit is made by judgment. The challenged patent can be maintained (if the lawsuit is dismissed) or be declared partially or wholly null and void (if the lawsuit is partially or completely upheld). A successful nullity action therefore leads to the revocation of the patent. The property right holder retroactively loses all legal positions previously based on the application.

The second and final appeal instance is the Federal Court of Justice.