The purpose of opposition proceedings before the European Patent Office is to give an opponent, which can be any member of the public, the opportunity to challenge the validity of a granted European patent.
Opposition to a European patent is a relatively cheap and quick way to clear the path to market in the face of invalid or dubious patent rights, and is an opportunity to revoke a European patent centrally. It has finality, in that a decision appealed to the EPO Boards of Appeal under normal circumstances cannot be appealed further.
When an opposition is filed, the opponent has to specify the extent to which the European patent is opposed, and the grounds on which the opposition is based, as well as indicating the facts and evidence presented in support of these grounds. This is considered to be of particular importance in that it gives the patentee a fair chance to consider its position at an early stage of the proceedings.
It is normal for an opposition to be filed against the patent as a whole, but even though in practice it is rather unusual that an opposition is limited to only a certain part (claims) of the patent, this possibility can be used by the opponent.
EPO, opposition proceedings