How to file an opposition at the European Patent Office (EPO)

An opposition to a European patent can be filed either in writing or electronically.

A signed notice of opposition may be submitted:

• in writing to the European Patent Office (EPO) in Munich, The Hague, or Berlin; or
• electronically using Online Filing 2.0 or the EPO Contingency Upload Service.

The opposition fee must be paid at the same time as filing, typically via debit order (automatic debiting is not available).

Grounds for opposition

You cannot challenge a patent for just any reason. The EPO only allows oppositions based on specific legal grounds set out in Article 100 EPC.

In simple terms, these fall into three main categories:

1. Lack of patentability

This ground applies where the invention does not meet the core patentability requirements under the EPC. For example, if it:

• is not new;
• does not involve an inventive step; or
• is not capable of industrial application.

It also includes cases where the subject matter is not considered a patentable invention at all, such as:

• mathematical methods or scientific theories;
• purely aesthetic creations;
• certain business methods or software;
• presentations of information.

Some inventions are excluded from patent protection altogether, including:

• inventions that would be against public order or morality;
• certain plant or animal-related inventions;
• medical treatment or diagnostic methods carried out on the body.

2. Insufficient disclosure

A patent may be opposed if it does not describe the invention clearly and completely enough for a skilled person to carry it out.

3. Added subject matter

This ground applies where the patent includes content that goes beyond what was originally disclosed in the application (or, where relevant, beyond an earlier parent application).

Key practical point

Each ground must be clearly identified when filing the opposition. The EPO's Notice of Opposition form (Form 2300) requires opponents to select each ground they intend to rely on.

What cannot be raised in opposition

Only the grounds listed in Article 100 EPC can be used in opposition proceedings. Issues such as lack of clarity, lack of unity, or an invalid priority claim cannot be raised as standalone grounds, even if they were discussed during examination.