European patent opposition at the EPO

Who can oppose, and when

Article 99(1) EPC gives "any person" nine months from the publication of the mention of grant in the European Patent Bulletin to file a notice of opposition. The opponent does not have to show any interest in the patent (Guidelines D-I 4). Several people can oppose jointly, and many patents attract more than one opponent. The only person who cannot oppose is the proprietor itself (G 9/93); a proprietor that wants to narrow its own patent uses central limitation under Art. 105a instead, which is not available while an opposition is pending.

A few points about the deadline catch people out:

• The notice is not deemed filed until the opposition fee is paid (Art. 99(1)). A notice filed in time with the fee paid a day late is inadmissible.
• An opponent cannot request re-establishment of rights if the period is missed (Guidelines D-III 1).
• You can oppose a patent that has already been surrendered or has lapsed in every state (Rule 75). That matters when damages for past infringement are still in play.
• Once the nine months are over, the only way into an EPO opposition is as an assumed infringer: if you are sued for infringement, or you sued for a declaration of non-infringement after the proprietor asked you to stop, you can intervene within 3 months of those proceedings starting, by paying the opposition fee (Art. 105, Rule 89).

An opponent with no residence or place of business in an EPC state must act through a European patent attorney (Art. 133(2)). That covers most US and Indian companies. The opposition is decided by an Opposition Division of three technical examiners, at least two of whom took no part in granting the patent, and the chair must be one of those two (Art. 19(2)).

The three grounds of opposition

Article 100 EPC is a closed list. An opposition may only be based on these grounds:

1. Art. 100(a), not patentable under Articles 52 to 57. In practice this is lack of novelty or inventive step in the large majority of cases, plus excluded subject-matter (for example a business method with no technical character) and the exceptions to patentability in Art. 53. Inventive step is argued with the problem-solution approach, explained in our guide to the problem-solution approach.
2. Art. 100(b), insufficient disclosure. The patent does not disclose the invention clearly and completely enough for a skilled person to carry it out across the whole scope claimed. This ground is common in chemistry and biotech, where a broad claim rests on a few worked examples.
3. Art. 100(c), added matter. The granted claims contain subject-matter that goes beyond the application as filed, typically a feature lifted out of its context in an example during examination. Added matter is a trap for the proprietor because of the next point.

Lack of clarity (Art. 84) and lack of entitlement are not grounds of opposition. Clarity can only be examined in claims amended during the opposition, and only to the extent the amendment introduces the problem (G 3/14). Since G 1/24 (18 June 2025), the description and drawings must always be consulted when the claims are interpreted for patentability, not only when a claim is unclear. That has made it harder to read a granted claim broadly to catch prior art the description plainly excludes.

The added-matter trap

Amendments in opposition must be occasioned by a ground of opposition (Rule 80), must not add matter (Art. 123(2)), and must not extend the protection conferred (Art. 123(3)). If a granted claim contains an added limiting feature, deleting it would broaden protection and keeping it offends Art. 123(2), so the patent can be lost with no way out. Good drafting at the application stage, with fallback positions written out in the description, is the best protection. Our guide on how to write patent claims covers how to build those fallbacks.

What the notice of opposition must contain

The notice is a written reasoned statement (Rule 76, Guidelines D-III 6). It must give the opponent's particulars, identify the patent, and state the extent to which the patent is opposed, the grounds, and the facts and evidence relied on.

Three of those elements cannot be fixed after the nine months: the fee and filing in time, a sufficient identification of the patent, and the substantiated statement of extent, grounds, facts and evidence (Rule 77(1), Guidelines D-IV 1.2.2.1). Missing particulars of the opponent can be corrected when the EPO invites you to (Rule 77(2)). So treat the nine-month date as the deadline for your whole case, not just the form: the extent of the opposition sets the frame for the rest of the proceedings, and grounds, facts and evidence filed later are treated as late-filed (Guidelines D-VI 1). The division may still examine a ground the opponent did not raise if it would prejudice maintenance of the patent (Rule 81(1)), but you should not count on it.

In practice the strength of an opposition is the strength of its prior art. Documents the examiner never saw, especially ones in a neighbouring field or in another language, are what move an Opposition Division. A prior art search done early in the nine months leaves time to buy translations, gather evidence of public prior use and write the inventive step attacks properly.

Fees for opposition and appeal

Official fees from the Rules relating to Fees in force from 1 April 2026:

The opposition fee is the same for everyone; the 30% micro-entity reduction in Rule 7a(3) does not apply to it. The reduced appeal fee is available to the categories listed in Rule 7a(2): microenterprises, SMEs, natural persons, non-profit organisations, universities and public research organisations. If the patent is maintained in amended form, the proprietor also pays the prescribed fee for publishing the new specification (Rule 82(2)).

Procedure and timeline

Opposition is a written procedure that normally ends in a single hearing. A typical case runs like this:

The proprietor's reply is the key document on its side. It usually defends the claims as granted as the main request and files a ladder of auxiliary requests, each narrower than the last, so that the division can maintain the patent at the highest level it finds allowable. The four-month period in Guidelines D-IV 5.2 is extended only in exceptional cases.

The summons comes with the division's preliminary opinion, and with it a final date for submissions, normally two months before the hearing (Guidelines D-VI 3.2, Rule 116). That date is not a time limit, so it cannot be extended. New requests and evidence filed after it need not be considered unless the subject of the proceedings has changed. Most of the real work happens in those last weeks before the final date.

Oral proceedings by videoconference

Oral proceedings before Opposition Divisions are held by videoconference. They are held on EPO premises only where there are serious reasons against videoconference, such as an inspection of an object whose feel matters, and general doubts about the technology do not count (Guidelines E-III 1.2, OJ EPO 2022, A106). A hearing usually takes a day. The division hears each request in turn, deliberates, and normally announces its decision at the end. If a party summoned does not attend, the hearing can go ahead without it (Rule 115(2)).

Accelerated opposition when there is litigation

Where an infringement or revocation action on the same patent is pending before the UPC or a national court, any party can ask for accelerated processing at any time, in a reasoned written request, and the EPO also accelerates when a court tells it about the action (Guidelines E-VIII 5, OJ EPO 2023, A99). If the EPO learns of the action during the opposition period, for example, the proprietor gets three months, not four, to reply, and the summons follows within two months of the reply at minimum notice. In every case the written decision follows within one month of the hearing.

Outcomes: what the EPO's figures show

Under Article 101, the division either revokes the patent, maintains it as amended, or rejects the opposition and leaves the patent as granted. The EPO Quality Report 2025 gives this split of opposition outcomes:

Read the other way round, about three oppositions in four end with the patent revoked or narrowed. The same report puts the opposition rate at 2.1% of granted patents in 2025, but it is uneven: 8.5% in agri-food, 3.1% in health, 0.5% in digital technologies. On timing, the mean duration in 2025 was 19.1 months against a target of 18, and 51.6% of oppositions were finished within 18 months, up from 38.1% in 2024. Around 42% of opposition decisions are appealed. These figures describe all oppositions; the odds in a given case depend on the prior art you have.

Appeal to the Boards of Appeal

Any party adversely affected by the Opposition Division's decision can appeal (Art. 107), and the appeal has suspensive effect (Art. 106(1)). A proprietor whose patent is revoked keeps it alive while the appeal runs. The deadlines are strict and the second one is the one that matters:

The appeal is a judicial review of the first-instance decision, not a second opposition. Under the Rules of Procedure of the Boards of Appeal (RPBA 2020, amended from 1 January 2024), the grounds of appeal and the reply must contain the party's complete case (Art. 12(3)), and anything not admissibly raised and maintained before the Opposition Division is an amendment the board may refuse to admit (Art. 12(4) and (6)). After the summons or the board's communication, new requests or evidence are in principle not taken into account at all unless there are exceptional circumstances justified with cogent reasons (Art. 13(2)). Put simply, the case you run before the Opposition Division is the case you will have on appeal.

Boards may hold oral proceedings by videoconference (Art. 15a RPBA); 62% of the 1,369 board hearings in 2025 took place that way (Boards of Appeal Annual Report 2025). The same report gives 2,220 appeals pending at the end of 2025, with 10.5% older than 24 months, and in 2025 the boards accelerated 39 appeals because of parallel proceedings, 19 of them at the UPC. Acceleration can be requested by a party, a national court or the UPC (Art. 10(3) to (6) RPBA).

Getting part of the appeal fee back

Settlements often happen during an appeal, and Rule 103 rewards withdrawing early: 100% back if the appeal is withdrawn before the grounds are filed and before the four months run out; 75% if withdrawn within two months of the board's communication announcing substantive examination; 50% if withdrawn within one month of the communication preparing the hearing; 25% if withdrawn later but before the decision is announced. Only one rate applies, the highest one available.

A board's decision is final. The only further step is a petition for review by the Enlarged Board under Art. 112a, limited to fundamental procedural defects such as a violation of the right to be heard. It must be filed within two months with a fee of €3,570, has no suspensive effect, and cannot be used to reargue the merits.

Opposition or UPC revocation action?

Since 1 June 2023 there is a second central route. The Unified Patent Court has exclusive jurisdiction over revocation actions and counterclaims for revocation of Unitary Patents and of classic European patents that have not been opted out (UPCA Art. 32(1)(d) and (e)). A standalone revocation action goes to the central division (Art. 33(4)), can be brought without any prior opposition (Art. 33(8)), and the grounds are those of Art. 138(1) EPC (Art. 65(2)). Our guide to the Unitary Patent and the UPC explains the court, the opt-out and the transitional period to 2030.

The two can run in parallel. Parties must tell the UPC about any pending opposition, and the court may stay its case if a rapid EPO decision is expected (Art. 33(10) UPCA). In the other direction, the EPO accelerates an opposition once it learns of UPC proceedings, as described above. A sensible default for a company worried about a competitor's patent: oppose within the nine months, because it is cheap and also covers EPC states the UPC never reaches, such as the UK, Spain and Switzerland, and keep UPC revocation for later, when you are sued or the patent starts to matter commercially.

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