Double patenting at the EPO: settled law, evolving practice?

The prohibition on double patenting at the European Patent Office (EPO) has long been recognised as a general principle of procedural law, notwithstanding the absence of any explicit provision in the European Patent Convention (EPC). While the Enlarged Board of Appeal has confirmed both the existence and the limits of that prohibition, recent developments under the EPO’s Convergence of Practice programme raise the question whether examination practice may now begin to edge beyond strictly identical subject-matter.

In March 2026, the Administrative Council of the European Patent Organisation approved a new “common practice as regards double patenting”.¹ Although formally non-binding, this document reflects a coordinated position among the EPO and participating national offices and is therefore likely to influence day‑to‑day examination going forward. The key issue is whether this common practice merely codifies existing law, or whether it signals a subtle – but potentially important – widening of the scope of the objection.

The established legal framework: identity of subject‑matter

The modern legal basis for the prohibition on double patenting at the EPO was firmly established by the Enlarged Board of Appeal in decision G 4/19. The Enlarged Board confirmed that an application may be refused if it claims the same subject‑matter as a European patent already granted to the same applicant with the same relevant date, relying on Article 125 EPC and generally recognised principles of procedural law. 

Importantly, both G 4/19 and subsequent Guidelines emphasise that the prohibition is limited to cases of identity. Overlapping or partially overlapping claim scope is not, in itself, sufficient. This approach has been consistently reflected in Board of Appeal case law (for example T 877/06) and is explicitly stated in the EPO Guidelines for Examination, which provide that “if the claims only partially overlap, no objection should be raised”. 

As a result, applicants have traditionally been able to pursue different claim formulations in parallel applications (for example parent and divisional, or priority and subsequent filings), provided that the claims were not substantively identical. This has allowed a degree of strategic flexibility, particularly in complex portfolios.

The convergence of practice initiative and double patenting

Against this background, the EPO’s Convergence of Practice programme seeks to reduce divergent approaches between the EPO and national patent offices by developing agreed “common practices” on selected topics, including double patenting. In March 2026, the Administrative Council unanimously approved common practices regarding double patenting put forward by the responsible working group. Implementation of the common practices is voluntary, but the approval signals broad institutional support and is likely to shape examination practice at the EPO in the near future. 

Content of the March 2026 common practice

The Common practice as regards double patenting (March 2026) reiterates the core principle that two patents with claims directed to the same subject‑matter cannot be granted to the same applicant or its successor in title. It also largely tracks the established situations in which double patenting may arise, namely:

• parent and divisional applications;
• an application and its priority application; and
• two applications filed on the same day by the same applicant.

Where the document goes further is in its articulation of how subject‑matter is to be compared. The common practice states that double patenting covers not only cases “where the respective applications contain claims explicitly including all of the same features”, but also situations where “the claims differ in their wording, but their subject-matter does not differ in substance”. 

An illustrative example is provided in which a claim referring to “Teflon” is considered identical in substance to a claim referring to “polytetrafluoroethylene (PTFE)”, because the terms allegedly describe “same material – only with a different name.”

Clarification or expansion?

At one level, this formulation may be seen as no more than an explicit acknowledgement of an implicit reality: purely verbal differences cannot permit double protection for the same invention. Few would argue that trivial rewording should circumvent the prohibition.

However, the introduction of the concept of “no difference in substance” could also be read as a potential broadening of the scope of the prohibition on double patenting. Unlike earlier guidance, which tended to focus on formal identity, the common practice invites a more substantive comparison between claims. This raises questions about where the boundary will be drawn in practice.

Notably, even the example chosen to illustrate “overlapping claims” is not entirely free from ambiguity. Teflon is a trade mark, whereas PTFE is a chemical descriptor. While the terms are often used interchangeably in practice, they are not, strictly speaking, identical in form or legal character. The fact that the example nonetheless treats them as the same material illustrates how quickly the analysis moves beyond literal claim wording and into questions of substance and characterisation. The document does not go on to suggest that genus-species relationships, functional versus structural definitions, or claims of differing breadth should be caught by the objection, and any such extension would sit uncomfortably with both G 4/19 and established Board of Appeal jurisprudence.

Nevertheless, the reliance on an example of this kind highlights that there is meaningful scope for disagreement over where the line is to be drawn between claims that are identical, claims that are “the same in substance”, and claims that merely overlap. Applicants and practitioners may therefore legitimately ask whether examiners will feel emboldened to argue identity of subject‑matter even where there is a real, albeit subtle, technical distinction. This risk may be particularly acute in technical fields where terminology is fluid, multiple descriptors coexist for the same concepts, or inventions can plausibly be characterised at different levels of abstraction.

Practical implications and outlook

For now, the safest reading of the March 2026 common practice is that it remains anchored to the long-standing principle of identity of subject‑matter, while seeking to prevent purely cosmetic claim differentiation. The EPO has repeatedly stated that partial overlap is insufficient, and there is no indication that this fundamental position has changed.

That said, as with many convergence initiatives, the true significance of the document will only become apparent through its application in examination. It will therefore be interesting to see:

• whether future revisions to the Guidelines are made in view of the common practice document;
• whether and how objections based on “overlapping claims” are raised; and
• whether any such objections withstand scrutiny on appeal.

In the meantime, applicants should continue to ensure that parallel claims are distinct in substance, not merely in language. While the new common practice does not represent a seismic shift, it does underline the importance of careful claim differentiation when structuring European patent families.

¹https://www.epo.org/en/legal/official-journal/report-186th-ac-meeting