According to the European Patent Convention (EPC), within 9 months from grant of a European patent, any third party may oppose it. In other words, any natural person or legal entity, other than the patent owner itself, may allege that the patent should never have been granted, and try to have the patent either limited in scope or revoked. This attack is a centralised one, applying to all designated states, so can be a very effective tool in securing freedom to operate.


Unfortunately, you can’t use just any arguments to try and attack a patent in opposition. For example, the ground of clarity cannot be used. The grounds of attack include the subject matter:

  • not being a patentable invention;
  • relating to matter excluded by A.53 EPC (i.e. under moral/public interest grounds);
  • not being novel;
  • not being inventive; and
  • not being capable of industrial application.

There are further grounds relating to sufficiency of disclosure (i.e. the patent doesn’t provide enough teaching to reproduce what is claimed), and/or that the claims extend beyond the content of the application as originally filed (i.e. matter has been added).


The notice of opposition, identifying the patent being opposed, as well as the opponent, must be filed within 9 months from grant of the patent. The notice must set out the grounds under which the patent is opposed, providing reasoned arguments, and also any documentary evidence (such as prior art) being relied upon. The opposition fee also has to be paid.

Once the opposition has been filed, the European Patent Office (EPO) checks that it meets formal requirements, before sending a copy to the patent owner, setting a 4-month period (usually extendible to 6 months) to file a response. In its response, the proprietor will usually file its own documents and arguments to support its position, but will also file a series of “auxiliary requests” which are alternative claim sets narrowed in scope to provide fallback positions should the OD consider any arguments of the opponent to have merit.

Once the patent proprietor has filed their response, the opposition division (OD – a set of 3 experienced EPO examiners) reviews the opposition and response.

Assuming that at least one of the parties has requested oral proceedings before a decision is taken, the OD will issue a summons to oral proceedings along with their preliminary opinion on the arguments raised. The summons will also set a deadline for the parties to file any further submissions (i.e. arguments, documents or auxiliary requests) before the hearing.

The OD will normally come to a conclusion as to whether the patent meets the requirements of the EPC at the hearing, announcing that decision. This may be that the patent is maintained as

granted, maintained in amended form (i.e. on the basis of one of the auxiliary claim requests filed) or is revoked. However, the reasons for that decision will not be given on the day, but will follow in written form at a later date.


Oral proceedings are essentially an opportunity for each party to make its arguments orally in front of the opposition division. Traditionally this has been done, in person, at the EPO premises in Munich or The Hague. However, since the covid-19 pandemic, these have generally been carried out by videoconference.

Depending on the size and complexity of the case (technology, number of opponents, number of documents) the hearing may be set for more than one day.

Usually the OD sets out what it wishes to talk about, the opponents then make their arguments, followed by the proprietor. Each party usually gets two opportunities to speak on a given subject before the OD retires to come to a decision on that aspect. As noted above, the OD will usually announce its decision on whether they consider the patent to meet the requirements of the EPC at the hearing.


EPO oppositions used to be quite a lengthy process, taking several years to conclude for anything but the most straightforward of cases. However, the EPO’s Early Certainty from Opposition initiative, introduced in 2016, aimed to reduce the average opposition duration from 19-27 months, down to just 15 months (including the typical 6-month gap between issue of the summons and oral proceedings).

In practice, we have seen quite a reduction in average duration for the cases we handle. This is supported by the EPO’s unwillingness to grant long extensions to the term for filing the proprietor’s response to the opposition, and the formation of more specialized opposition divisions.

When the covid-19 pandemic hit, face to face hearings were largely cancelled, leading to a backlog of cases. However, oral proceedings by VC were started, and the EPO has been working hard to catch up since.


As with other decisions made by departments of first instance at the EPO, decisions of opposition divisions can be appealed to the boards of appeal. The boards of appeal focus on the legal correctness of the first instance division, and generally avoid considering new facts/arguments not already considered by the department of first instance.

Any notice of appeal must be filed within two months from notification of the decision being appealed (and the appeal fee paid), with the substantiated grounds of appeal to be filed within four months from notification of the decision being appealed.


The opponent has to be named in any opposition, and so it is necessary to consider whether the opponent wishes to reveal itself to the patent proprietor, when previously it may have been able to work the invention “under the radar”, or even avoid expensive license terms. However, it is possible to mitigate this by filing the opposition in the name of a straw man. There are third party entities that provide this service, or you could file in the name of a friend or attorney.

Given the possibility for a patent to be maintained in amended form, there is the risk that a patent might be stronger following opposition, than prior to opposition. In other words, amendments may be made during opposition that make a potentially previously invalid patent valid. Given that the grounds of opposition may be more limited than grounds that might be raised during national litigation, one should consider the merits of filing an opposition versus national litigation. Of course, opposition allows a patent to be attacked in all designated states in one go, rather than filing court actions on a country-by-country basis. As such, opposition costs are usually at least an order of magnitude lower than the corresponding cost of filing national revocation actions in each country of interest.


Our team has extensive experience in opposition matters, across most fields of technology. We have supported small start-ups through the process, and are also used by large multi-national companies, both defending their key assets and actively opposing third party patents to secure freedom to operate. We have defended against multiple opponents as well as collaborated with co-opponents to secure optimal outcomes for our clients. We also have considerable experience of videoconference oral proceedings, including with the use of simultaneous interpretation.

Many of our opposition team also have in-house experience, so are acutely aware of the pressures faced by in-house attorneys, and are able to make full use of any in-house resources available to ensure an optimal and cost-effective outcome.

If you have any questions, or would like advice on a specific case, please contact your usual Greaves Brewster attorney.