EPO Opposition: What a US Patent Owner Needs to Know

A European patent matters to a US business in two situations: a patent you own in Europe comes under attack, or a competitor's newly granted European patent blocks your product in the EU. In both cases the EPO opposition procedure is the central tool — and in both cases the decisive variable is the same: a nine-month window from the date the grant is published in the European Patent Bulletin.

Scenario 1 — defending your own European patent. A third party has filed an opposition against your EP patent, usually on grounds of lack of inventive step or added subject matter. You have four months from notification to file a substantive response. The realistic outcomes are: the opposition is rejected and the patent stands; the patent is maintained in amended form (narrower claims, but still enforceable); or the patent is revoked for all designated states at once. A well-prepared response that refiles tighter claims and fixes formal issues is often enough to keep a commercially valuable core claim alive.

Scenario 2 — attacking a competitor's European patent. Any person (including a company you control or an ally) can oppose within nine months of grant. A successful opposition can remove the patent centrally — for every country where it was validated — in a single proceeding. That is the key difference from the US: there is no need to run parallel invalidity actions in Germany, France and Italy. If the window has already closed, the fallback is national revocation actions or a UPC revocation, which cost more and run country by country or before one central court.

The nine-month deadline is absolute. The period runs from the publication of the grant (not from the priority date, the filing date or the date you learned of the patent). There is no extension, no grace period and no restoration. This is why monitoring competitor grants matters: the practical workflow for a US company is to watch the European Patent Bulletin for grants in its field, calendar the nine-month date immediately, and start the prior-art review as early as possible — an opposition filed in month eight with weak evidence is worse than one filed in month three with the right references.

The grounds are limited to patentability issues. Under Article 100 EPC an opposition can only be based on: the patented invention lacking novelty or inventive step; the subject-matter extending beyond the content of the application as filed; or insufficient disclosure. Commercial arguments, competitive harm, inequitable conduct and litigation-history grievances play no role before the EPO — a common adjustment for US counsel. The opposition stands or falls on dated prior art and a clear technical argument about what a skilled person would have done.

What an opposition costs. The table above shows the timeline and indicative figures. The official opposition fee is €880 and a straightforward opposition is typically handled for a fixed attorney fee of €1,200 covering the grounds, the evidence set and the filing. The proprietary side of a well-managed case — response, possible claim amendments and attendance at oral proceedings — usually lands in the €2,500–€5,000 range in total. Compare that with a single national invalidity action in Germany, which alone often exceeds the entire opposition, and the economics for a multi-country threat become obvious. The unsuccessful party may in principle be ordered to bear the costs of the opposition, but this is discretionary and modest compared with US-style fee-shifting — budget as if each side pays its own.

The procedure differs from US practice in other ways. There is no discovery: you present your evidence with the notice of opposition or response, and later amendments to your case are restricted. There is no jury and no damages — the opposition decides only validity, and enforcement (injunctions, damages) happens separately in national courts or at the UPC. Claim construction follows the EPC and EPO case law, which differs from US practice: the claims are interpreted through the description, and the standard is closer to a purpose-bound reading than to a purely literal or purely prosecution-history-driven one. The procedural differences are covered in the EPO vs USPTO practice guide.

How US counsel and the European Patent Attorney work together. The opposition must be filed and prosecuted by a European Patent Attorney before the EPO; US patent counsel cannot appear directly. In practice the division of labour is: US counsel owns the business case, the litigation strategy and the client relationship; the European attorney owns claim construction under the EPC, the prior-art attack or defence, the amendment strategy and the procedural deadlines. The best results come when the two coordinate on the evidence set before anything is filed — an opposition is a one-shot window, and a weak first filing can make a later, better case harder to argue.

Common mistakes to avoid. Filing just inside the deadline with whatever prior art is at hand. Arguing commercial harm instead of patentability. Ignoring the four-month response deadline after your own patent is opposed — inaction leads to revocation by default, not to a neutral outcome. And treating oral proceedings as optional: since 2016 the Opposition Division is expected to summon oral proceedings if the case is not decided on the written record, so attendance and argument are part of the budget, not an extra.

If a European patent has been granted against your product, or your own EP patent has just been served with an opposition, send the patent number and the grant-publication date to docket@bauerip.com — you will get an assessment of the grounds and a fixed-fee quote within one business day. The mechanics of the procedure are described in the EPO opposition guide, and the full representation service is on the European Patent Attorney page. If you need hands-on help, see European patent attorney for US companies.