Following publication of the European patent application under Art. 93, any person may present observations concerning the patentability of the invention. Such observations must be filed in writing and must include a statement of the grounds on which they are based. That person may not be a party to the proceedings before the EPO. The statement of grounds must be presented in English, French or German. Although the third party is sent acknowledgment of the receipt of his observations, the EPO does not inform him of any further action it takes in response to them.

The observations are communicated to the applicant or proprietor without delay and he 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, i.e. they must be admitted to the proceedings. If the observations relate to alleged prior art available other than from a document, e.g. from use, this should be 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 conclusion of proceedings will not be taken into account and will simply be added to the file.