Under Art. 105 EPC, to intervene admissibly in opposition proceedings a party must show either that proceedings for infringement of the same patent have been instituted against him, or that following a request of the proprietor of the patent to cease alleged infringement, the third party has instituted proceedings for a ruling that he is not infringing the patent. Under Art. 105(2) EPC, an admissible intervention shall be treated as an opposition.
In the course of the revision of the EPC, Art. 105 EPC was redrafted to clarify its meaning. The word 'court' has been deleted entirely, since an action for declaration of non-infringement need not be instituted before a court in all states. The details relating to intervention have been transferred to the Implementing Regulations (see R. 89 EPC).