Following the grant of a European patent, there is a window of nine months – the so-called "opposition period" – during which oppositions can be filed against a granted patent and the revocation of the patent can be requested. The grounds for opposition are:

  • lack of novelty;
  • lack of an inventive step;
  • lack of sufficiency of disclosure; and
  • extension of the patent beyond the content of the application as originally filed.

If any of these grounds apply, the European Patent Office (EPO) revokes the patent.

The current practice of the EPO allows an opposition to be validly filed by a "straw man" – that is, by an opponent filing the opposition not in their own interest, but in the interest of an anonymous third party. Typically, in these cases, a law firm acts as the opponent and the representative at the same time, to protect the identity of the client. This practice has been challenged numerous times over the years, most recently in the case underlying decision T 1839/18, in which the Board of Appeal confirmed the legality of the practice.


In the opposition appeal proceedings underlying decision T 1839/18, the patent owner challenged the admissibility of the opposition. The patent owner argued, among other things, that the opponent had no legitimate interest in filing the opposition. In support, the owner referred to the Enlarged Board of Appeal decision G 1/06, which the owner interpreted as stipulating a general requirement for a "legitimate interest" in any procedural act taken before the EPO.


The Board in T 1839/18 did not follow the owner's interpretation. Rather, the Board emphasised that essentially any filed opposition was in the interest of the public by:

  • revoking undeserved monopolies or reducing them to the actually deserved scope;
  • fostering industrial development by preventing innovation from being led astray by wrongfully granted monopolies; and
  • enhancing legal certainty.

In the end, the Board found that the term "straw man" is in fact misguided, since no interest in filing an opposition has to be proven.

In conclusion, the Board confirmed the established practice of filing an opposition at the behest of a third party, whose identity is not revealed, without indicating this fact to the EPO.


There are many reasons for filing anonymous oppositions at the EPO. For instance, potential infringers may want to move against a patent without alerting the patent owner to their potentially infringing activities. Sometimes the reason for filing an anonymous opposition is to protect commercial relationships with the patent owner. Anonymity also helps to avoid any arguments made during opposition proceedings being held against the potential infringer in later infringement proceedings.

Keeping anonymity sometimes comes at a price. For instance, attending oral proceedings with a professional representative may not be possible without revealing the identity of the interested third party. More relevantly, a party may be unable to make certain requests that can be justified only by an interested third party.

For example, an anonymous third party may be unable to make a request for expedited proceedings if the reason for expediting the proceedings relates only to the anonymous third party. In case T 872/13, a request for expedited proceedings was denied because the underlying grounds that could have justified accelerating the processing did not pertain to the straw man opponent, but to a company that was not party to the proceedings. Maintaining anonymity may also reduce the probative value of experimental evidence if it prevents the identity of the person that has carried out the experiments from being revealed (T 103/15).

Oppositions can be filed anonymously with the EPO by making use of a straw man opponent. Straw man oppositions can be helpful to protect commercial interests. However, oppositions may also have negative consequences. Therefore, it is important in each individual case to weigh the benefits of staying anonymous against the potential pitfalls.

For further information on this topic please contact Markus Grammel at Grünecker by telephone (+49 89 21 23 50) or email ([email protected]). The Grünecker website can be accessed at