Submit prior art to the European Patent Office

The European Patent Convention allows any person to submit prior art at the European Patent Office. There are two procedures: one before the patent is granted (the “observations” procedure), the other within 9 months after the patent is granted (the “opposition” procedure).

The official languages of the European Patent Office are English, French and German. You should provide translations to one of these languages for documents in other languages.

0. Which prior art references can you submit?

Two conditions are absolutely necessary for a document to constitute prior art:

  • the document must have been made available to the public

  • the publication date is paramount in order for prior art to be relevant for challenging patent validity, so any document where the publication date is uncertain is going to have less value.1

In order to constitute prior art and establish that the patent application claims something that is not new, the publication date must precede the patent application filing date and its priority date.

1. The EPO observation procedure

The observation procedure starts after the publication of the European patent application (according to article 93) and ends when such application is granted. The EPO guidelines specify that:

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 (3), 53 or 57) and unallowable amendments (Art. 76(1), 123(2)).

Third-party observations can be submitted online directly to the EPO.

2. The EPO opposition procedure

The opposition procedure is much more complex. A third-party filing a notice of opposition will become a party to the procedure.

Any person may oppose a patent within 9 months of the publication of the mention of the grant in the European Patent Bulletin. The formalities of the opposition notice are set forth in rule 76.

(a) particulars of the opponent as provided in Rule 41, paragraph 2(c);

(b) the number of the European patent against which opposition is filed, the name of the proprietor of the patent and the title of the invention;

(c) a statement of the extent to which the European patent is opposed and of the grounds on which the opposition is based, as well as an indication of the facts and evidence presented in support of these grounds; […]


The procedure is not admitted until the fees are paid:

[…] Each party to the opposition proceedings shall bear the costs it has incurred, unless the Opposition Division, for reasons of equity, orders, in accordance with the Implementing Regulations, a different apportionment of costs. […] (article 104).

These rules are set forth in rule 88.

(1) The apportionment of costs shall be dealt with in the decision on the opposition. Such apportionment shall only take into consideration the expenses necessary to assure proper protection of the rights involved. The costs shall include the remuneration of the representatives of the parties.

(2) The Opposition Division shall, on request, fix the amount of costs to be paid under a final decision apportioning them. A bill of costs, with supporting evidence, shall be attached to the request. Costs may be fixed once their credibility is established.


Oppositions may be submitted online.

Find relevant patent and patent applications

You can search through the EPO’s patent database. You can also search through the classification to find relevant classes.


  1. Where the actual publication date of a document is not known, you will have to provide evidence to establish when the document was publicly available. ↩