European Patent Office (EPO) oppositions can feel unfamiliar even for experienced attorneys, particularly US patent counsel. That unfamiliarity does not stem from a lack of substantive expertise, but from the procedural differences between European oppositions and US post-grant proceedings. The main point is that EPO oppositions are front-loaded, so early actions and decisions can be especially consequential.

From the filing of an opposition through written exchanges and oral proceedings before the Opposition Division, a first-instance decision typically takes 18 to 30 months. If the case proceeds to appeal, a further two to three years is common. An opposition must be filed within nine months of grant, and what the opponent files in that initial window, together with the patentee’s response, can shape the next three to five years of proceedings. In practice, this influence can extend all the way to a final decision on appeal and the remainder of the patent’s life.

Why early choices matter

Early choices around evidence, claim amendments and fallback positions, the so-called auxiliary requests, can have long-term consequences. In proceedings before the Opposition Division, deficiencies cannot always be reliably remedied later, particularly where evidence or amendments are introduced only at a late stage. Admissibility is increasingly scrutinised, and submissions are expected to be made at the earliest opportunity. This is especially true for evidence, and any late-filed material must be clearly relevant on its face to have a realistic prospect of being admitted.

By the time a case reaches appeal, introducing new claim requests or new lines of argument will usually no longer be possible. This can often be a point of surprise for applicants and instructing parties. Appeal proceedings before the Boards of Appeal are a judicial review of the first-instance decision, not a second bite at the cherry. Admissibility standards on appeal are strict, particularly for claim requests, arguments, or evidence that were not properly developed at first instance. In practice, if something was not credibly on the table during opposition proceedings, it is unlikely to be considered on appeal.

This is why a well-run EPO opposition must be appeal-aware from the outset, ensuring that evidence, arguments and claim requests are introduced as soon as possible to remain admissible later. For instructing parties, including in-house or overseas counsel, recognising this and engaging early can be the difference between winning on the merits of the case and finding that options for continuing to defend or attack have become increasingly limited over the course of the proceedings.

Practical takeaways: how to stay in control early

The key takeaway is that EPO oppositions reward early decision making. In practical terms, this means investing early effort in areas that are difficult or impossible to fix once an opposition is underway.

Where claim amendments are likely, fallback positions should be proposed and assessed early for their commercial viability. Depending on which side you are on, this may include considering whether proposed amendments leave meaningful freedom to operate or enforceable scope. For an opponent, this early work should include identifying and securing relevant evidence at an early stage. This may involve validity searches, but also consideration of other forms of evidence, for example through early engagement with R&D or sales teams to uncover documentary or physical evidence of prior use that may not be apparent from the patent record alone.

Conclusion

Ultimately, the EPO expects parties to put their case forward early. Decisions taken shortly after grant can determine what arguments, evidence, and claim requests will still be available years later, including on appeal. Recognising this at the outset is key to maintaining procedural options later in the proceedings.

This article was written by Senior Associate, Dr Alex Colman. If you would like to discuss EPO opposition or appeal proceedings, or the impact of early procedural decisions, please contact alex.colman@wilsongunn.com or your usual Wilson Gunn attorney.