Rule 42 EPC: Content of the description

Text of Rule 42 EPC

In plain English

Rule 42 sets the six building blocks of a European description and, by default, their order: technical field, background art, the invention as claimed (problem, solution and advantages), a brief description of the figures, a detailed way of carrying out the invention, and industrial application where that is not obvious.

Rule 42(1)(c) is the one with consequences. The EPO judges inventive step with the problem-solution approach, so a description that explains the technical problem and the effects of the features gives you material to argue from. Effects you never mentioned are harder to rely on later; G 2/21 allows a technical effect to be relied on only if the skilled person would derive it as encompassed by the technical teaching and embodied by the invention as originally disclosed.

Rule 42(1)(b) leads to a routine request in examination: the examining division asks you to acknowledge the closest prior art found in the search in the background section. The Guidelines let the examiner add such a summary in the Rule 71(3) text without consulting you (C-V, 1.1).

At grant, the description is also expected to match the claims. Statements of invention are brought into line with the allowed claims, and embodiments outside the claims removed or marked. T 56/21 found no basis in Rule 42 or Article 84 for insisting on this; G 1/25 (3 September 2026) held that adaptation is required where an inconsistency means Articles 52 to 57, 76(1), 83, 84, 123(2) or 123(3) are not met.

Because Article 123(2) limits later amendments to what the application as filed discloses, the description is also your reservoir of fallback positions. Anything not in it on the filing date cannot be added.

Key decisions

• G 2/21 (Plausibility) : An applicant may rely on a technical effect for inventive step if the skilled person, from the application as filed, would derive it as encompassed by the technical teaching and embodied by the original invention.
• T 1989/18 (Adaptation of the description/HOFFMANN-LA ROCHE) : Held that neither Article 84 nor Rules 42 and 48 gave a legal basis for refusing an application because the description had not been adapted to the claims; one side of the split later resolved by G 1/25.
• G 1/25 : Where amended claims create an inconsistency with the description that leads to non-compliance with the listed Articles, the description must be adapted.

Common objections

Closest prior art not acknowledged

Add a short, neutral summary of the closest document in the background section. Do not add new technical information about your invention while doing so.

Statements of invention broader than the claims

Bring passages such as “the invention provides…” into line with the allowed claims, and mark embodiments that are no longer covered.

Drafting and prosecution tips

• State the problem in technical terms and tie each key feature to an effect, because the problem-solution approach will be built on what you wrote.
• Describe features generally and in combinations, not only inside one detailed embodiment, so that later claim amendments have a clear basis.
• Keep background art factual and short; Rule 48(1)(b) prohibits disparaging statements, although plain comparisons with the prior art are allowed.