Following publication of the European patent application under Art. 93, any person may present observations concerning the patentability of the invention. Although lack of novelty and/or inventive step are the most common observations, third-party observations may also be directed to clarity (Art. 84), sufficiency of disclosure (Art. 83), patentability (Art. 52(2) and Art. 52(3), Art. 53 or Art. 57) and unallowable amendments (Art. 76(1), Art. 123(2) and Art. 123(3)).[Art. 115; Rule 114(1); ]

Such observations must be filed in writing in English, French or German and must include a statement of the grounds on which they are based. The person filing them may not be a party to the proceedings before the EPO. The web interface provided by the EPO is the preferred means of filing such observations (see OJ EPO 2017, A86).

Documentary evidence and, in particular, publications submitted in support of the arguments may be filed in any language. However, the EPO may request that a translation into one of its official languages be filed within a period to be specified; otherwise the evidence will be disregarded.[Rule 3(3); ]

Although third parties are sent acknowledgment of the receipt of their observations (if these were not filed anonymously), the EPO does not specifically inform them of any further action it takes in response to them. However, the outcome of the evaluation by the competent division will briefly be indicated in the respective office action from the EPO (e.g. in a communication or in the intention to grant) and will thus be visible to the public.

The EPO will make every effort to issue the next office action within three months of receipt of third-party observations under Art. 115 by the examining division, provided the observations are substantiated and have not been filed anonymously. Where the observations are received at a time when a reply from the applicant to a communication is outstanding, this period starts from receipt of the reply at the EPO.

The observations are communicated to applicants or proprietors without delay and they may comment on them. If they call into question the patentability of the invention in whole or in part, they must be taken into account in any proceedings pending before a department of the EPO until such proceedings have been terminated. If the observations relate to alleged prior art available other than from a document, e.g. from use, this is taken into account only if the alleged facts either are not disputed by the applicant or proprietor or are established beyond reasonable doubt. Observations by third parties received after the decision to grant/refuse the application has been pronounced in oral proceedings or issued in written proceedings (see G 12/91) will be included in the file without taking note of their content. Observations by third parties received once proceedings are no longer pending (e.g. after publication of the mention of the grant) will be neither taken into account nor made available for file inspection. They will however be made available for file inspection upon the start of opposition proceedings.[Rule 114(2); ]

The EPO will generally apply the practice regarding third-party observations filed in the Euro-direct procedure mutatis mutandis to third-party observations filed during the international phase upon entry of the Euro-PCT application into the European phase.

Where a third-party observation was filed during the international phase, the EPO as designated/elected Office will consider its content upon entry into the European phase once this becomes available to it. The examining division will make every effort to issue the next office action within three months after expiry of the period under Rule 161 EPC, but only on condition that the third party has clearly expressed its wish to achieve expedited treatment in the European phase, that the observation was filed non-anonymously and that it was substantiated. A third party wishing to achieve such a result in the European phase must, therefore, make this clear in the observation or file the observation with the EPO as designated/elected Office.