2.2. When can third-party observations be filed?

Article 115 EPC specifies that observations cannot be filed until after publication of the European patent application but sets no upper time limit for their presentation by persons wishing to make adverse observations concerning the patentability of inventions claimed in patent applications/patents. This means that observations can also be filed during opposition proceedings, even after expiry of the opposition period, and during appeal proceedings (T 390/90, G 9/91, OJ 1993, 408, T 1756/11, T 2255/15, T 972/22). Art. 115 EPC explicitly covers all proceedings before the EPO and so applies, in principle, to revocation and limitation proceedings too.