Unity of invention is a requirement that affects European patent applications. Complications with unity of invention sometimes arise when European patent applications are based on patent specifications that have been drafted primarily based on requirements in jurisdictions other than Europe. Understanding European patent practice on unity of invention may therefore provide greater certainty with respect to what can be covered by a European patent application.
This article digs into some of the legal aspects of unity of invention and provides some tips for navigating unity of invention.
How is unity of invention assessed for European patent applications?
Unity of invention relates to the general principle that a European patent is granted for each invention separately.
For example, this principle assists to provide equal treatment of applicants of European patent applications since any applicant is entitled to the same service (e.g., a European patent for a single invention) for the same official fees [1].
What is the legal basis for unity of invention?
Unity of invention is governed by Article 82 and Rule 44 of the European Patent Convention (EPC).
Article 82 of the EPC requires that a “European patent application shall relate to one invention only or to a group of inventions so linked as to form a single general inventive concept” [2].
In practice, this essentially requires that the claims of a European patent application are required to relate to:
- one invention only; or
- to a group of inventions so linked as to form a single general inventive concept.
Rule 44 EPC governs the scenario in which the claims are directed to a group of inventions.
What is a group of inventions?
A group of inventions may be formed, for example, by:
- a plurality of independent claims in the same claim category (e.g., product, process), or in different claim categories,
- a plurality of alternative inventions defined within a single independent claim, or
- a plurality of dependent claims where the independent claim is either not novel or not inventive [3].
How is a group of inventions assessed?
As mentioned previously, Rule 44 EPC governs the scenario in which the claims are directed to a group of inventions.
Rule 44 EPC recites that:
“Where a group of inventions is claimed in a European patent application, the requirement of unity of invention under Article 82 shall be fulfilled only when there is a technical relationship among those inventions involving one or more of the same or corresponding special technical features”.
Rule 44 EPC defines “special technical features” as features which define a contribution which each of the claimed inventions considered as a whole makes over the prior art.
In other words, if a group of inventions is claimed, the requirement that the inventions in this group be so linked as to form a single general concept is fulfilled only if there is a technical relationship between the claimed inventions involving one or more of the same or corresponding special technical features [3].
For additional detail, the EPO Guidelines Part F, Chapter V, Section 3 provides a three-step process for substantively assessing unity of invention [4].
What does the term “special” mean?
The term “special” means that the features in question define the contribution that the invention considered as a whole makes over the “prior art at hand” in terms of novelty and inventive step.
In other words, a “special” feature, is a feature that is novel and inventive over the cited prior art [3].
What do the terms “same” and “corresponding” mean?
The distinction that features do not have to be the “same” but can be “corresponding” is an important distinction when assessing unity of invention.
The term “same” means that the special technical features are identical or define an identical chemical structure.
The term “corresponding” means that the special technical features achieve the same technical effect or solve the same technical problem.
What are examples of “corresponding” features?
Correspondence may be found in alternative solutions or interrelated features.
For example, the interaction between a plug and a socket causing a releasable electrical connection, or in a causal relationship such as a step in a manufacturing process that causes a certain structural feature in a product.
An application might include two sets of claims, one comprising a metal spring and another comprising a block of rubber. The metal spring and block of rubber may be considered to be corresponding technical features as they both achieve the same technical effect of resilience [3].
How can this affect a filing strategy?
European divisional patent applications can be relatively expensive, for example, in comparison to a US continuation patent application.
In order to potentially avoid filing a more expensive European divisional patent application, it may be worth considering whether the subject-matter of such a divisional application could also be covered by the existing European patent application. For example, if the claims of the divisional applications produce the same technical effect or solves the same technical problem as the existing patent application, a divisional application may not be required.
Is unity of invention a ground of opposition?
No.
The requirement of unity of invention only applies to European patent applications and not to European Patents.
How can we help?
As specialists in European patent practice, we can prepare and prosecute European patent applications to help you attempt to take of advantage of unity of invention.
Please get in touch with Thomas Measures – Appleyard Lees if you would like to discuss this further.
References:
[1] – https://www.epo.org/en/legal/guidelines-epc/2025/f_v_1.html
[2] – https://www.epo.org/en/legal/epc/2020/a82.html
[3] – https://www.epo.org/en/legal/guidelines-epc/2025/f_v_2.html
[4] – https://www.epo.org/en/legal/guidelines-epc/2025/f_v_3.htm
