Harmonizing Claim Interpretation at the EPO

Introducing EBoA decision - G1/24

On 18 June 2025, the Enlarged Board of Appeal (EBoA) of the European Patent Office (EPO) issued its landmark decision in case G 1/24 (“Heated Aerosol”). This decision addresses fundamental questions about how patent claims should be interpreted during patentability assessments, resolving divergent approaches in prior case law. The EBoA confirmed that patent claims must always be interpreted in light of the description and drawings when assessing patentability, not only in cases of ambiguity. This clarification brings EPO practice into closer alignment with national courts and the new Unified Patent Court (UPC).

Being generally nerdy we got around to analyze the legal reasoning behind G 1/24, including its doctrinal underpinnings in the European Patent Convention (EPC), and discuss the decision’s practical implications for European small and medium-sized enterprises (SMEs) in their patent filing, prosecution, and litigation strategies.

Divergent Approaches to Claim Interpretation

Under the EPC framework, Article 69 EPC (and its Protocol on Interpretation) provides that a patent’s extent of protection is determined by the claims, “nevertheless, the description and drawings shall be used to interpret the claims”.

However, Article 69 is located in the EPC chapter on patent effects (infringement), not examination, raising the question of whether it applies to claim interpretation during EPO patentability analysis.

Separately, Article 84 EPC requires that claims be clear, concise, and “supported by the description”, implying a relationship between claim language and the description.

In practice, these provisions led to divergent case law on claim construction before grant: some EPO Boards of Appeal always consulted the description to interpret claims, whereas others consulted it only if a claim was unclear or ambiguous on its face.

This inconsistency came to a head in the T 0439/22 appeal (Philip Morris v. Yunnan Tobacco) concerning a patent for a vaping device. The case turned on whether the term “gathered sheet” in the claim should be given its usual, narrow meaning (which preserved novelty) or a broader meaning given by the description’s explicit definition (which would destroy novelty). Recognizing the lack of uniform guidance on whether and how to use the description for claim interpretation in such patentability questions, the Technical Board referred three questions of law to the Enlarged Board (G 1/24).

Legal Reasoning and Key Doctrines

In G 1/24, the Enlarged Board addressed two admissible questions (the third was deemed encompassed by the second) and used them to articulate general principles of claim interpretation under the EPC. Crucially, the EBoA found no single EPC article that serves as an exclusive legal basis for claim construction during patentability analysis. It noted that Article 69 EPC and its Protocol were “arguably only concerned with infringement actions” and thus not an ideal basis for examination-stage interpretation. On the other hand, Article 84 EPC is a formal provision about claim drafting (clarity and support) and “provides no guidance on how to interpret claims” once drafted.

Indeed, prior Enlarged Board cases had pointed to both Article 69 (e.g. G 2/88, G 6/88) and Article 84 (e.g. G 2/12) as potential bases, but in none was the choice of legal basis outcome-determinative. Confronted with this ambiguity, the Enlarged Board in G 1/24 declined to anchor claim interpretation in either article alone. It gave the “strictly formal answer” to Question 1 that no explicit EPC article fully governs claim interpretation for assessing patentability.

Instead, the EBoA derived guiding principles from the established case law of the Boards of Appeal. It observed that, regardless of legal basis, boards generally agreed on two fundamental points.

1. Claims as the Basis: “The claims are the starting point and the basis for assessing the patentability of an invention under Articles 52 to 57 EPC.” In other words, the claimed features define the scope of the invention to be tested for novelty, inventive step, etc.; this principle was undisputed in the case law and reaffirmed by the Enlarged Board.

2. Always Consult the Description: “The description and any drawings shall always be consulted to interpret the claims when assessing the patentability of an invention … and not only if the person skilled in the art finds a claim to be unclear or ambiguous when read in isolation.” This directly answers Question 2, rejecting the contrary line of cases that limited recourse to the description only to resolve ambiguity. The Enlarged Board emphasized that determining a claim to be “clear” is itself an act of interpretation – one cannot avoid consulting the context by claiming the claim is self-explanatory.

The decision’s reasoning invokes key EPC interpretative doctrines and precedent. G 1/24 expressly cited Article 69 EPC’s wording and principles: while Article 69 may technically be aimed at infringement contexts, its principle (that claims are interpreted with the aid of the description) reflects a general interpretive approach that should logically extend to patentability analysis as well. The EBoA noted it would be “most unattractive” for the EPO to apply a different claim interpretation approach from that of courts “downstream” that enforce the patents. This resonates with the “harmonisation philosophy” underlying the EPC, as recognized in earlier Enlarged Board cases (e.g. G 5/83, G 3/08).

Furthermore, the Enlarged Board referenced recent UPC case law confirming the same interpretive rule. In particular, the UPC Court of Appeal in NanoString v. 10x Genomics (Feb 2024) held that “the description and the drawings must always be used as explanatory aids for the interpretation of the patent claim and not only to resolve any ambiguities”, mirroring the approach now adopted by G 1/24. By aligning EPO practice with that of the UPC and national courts, the decision strengthens consistency in the European patent system.

Another doctrinal point in G 1/24 is the reinforcement of clarity (Article 84 EPC) as a pre-grant safeguard. The EBoA cautioned that its ruling should not be seen as a license to tolerate unclear claims on the premise that examiners or courts can later “interpret them” using the description. On the contrary, the decision underscores that any lack of clarity in a claim should be resolved by amendment during examination. In the Enlarged Board’s words: “The correct response to any unclarity in a claim is amendment.” Examiners are thus encouraged to police clarity rigorously and applicants must draft and amend claims carefully, rather than hoping to resolve ambiguities by interpretation post hoc. This aspect of the reasoning highlights the EPO’s commitment to high-quality examination and reflects comments made by the EPO President during the referral.

Implications for SMEs’ Patent Filing and Prosecution Strategies

Small and medium-sized enterprises (SMEs) which often operate with limited IP budgets and resources should pay particular attention to the practical lessons of G 1/24 for how they draft and prosecute patent applications in Europe. The decision’s clarifications impact the entire lifecycle of a patent, from initial application to examination, opposition, and enforcement:

Patent Drafting and Filing: SMEs must ensure that their patent descriptions are drafted with the same precision and forethought as their claims. Under G 1/24, any definition or detail in the description can influence how claims are construed. Inconsistencies or overly broad definitions in the description may later broaden or narrow the claim scope in unintended ways, potentially jeopardizing novelty or limiting protection. For example, if a term has a customary technical meaning but the description provides a different or broader definition, the description’s definition will be taken into account.

SMEs should therefore invest time in drafting clear definitions and aligning the description with the intended claim scope. Even boilerplate language or careless phrasing in the description can be “seized upon” by opponents once the description is always consulted. Notably, relying heavily on automated drafting tools (like AI!!!) without careful human review could be risky, as such tools might introduce inconsistencies between claims and description Ultimately, a well-drafted application post-G 1/24 means fewer vulnerabilities for challengers to exploit and greater certainty in claim meaning from the outset.

Examination and Prosecution: During EPO prosecution, SMEs should be prepared for examiners to place more emphasis on claim interpretation issues and description amendments. While the immediate examination process may not dramatically change overnight, G 1/24 arms applicants with a clear legal basis to discuss how the description affects claim scope. Examiners may also become more stringent in raising clarity objections under Article 84 EPC, knowing that any latent ambiguity will necessitate interpretation and could complicate validity later.

The Enlarged Board’s endorsement of thorough clarity examination suggests that applicants might face increased pressure to amend claims for clarity and to adapt the description to the allowed claims. Indeed, the EPO’s existing practice of requiring applicants to adapt the description prior to grant (to excise inconsistencies or over-broad statements) will likely be reinforced. An SME should budget both time and resources for potentially iterative description amendments in prosecution, and approach them cautiously.

Every addition or deletion in the description during examination should be reviewed for how it might alter claim interpretation or possibly introduce “added matter” beyond the original disclosure G 1/24 effectively puts applicants on notice that shortcuts in prosecution (such as leaving ambiguous wording in place, or neglecting to update the description) can backfire once the patent is enforced or challenged. Conversely, a carefully prosecuted patent, with a clear and consistent specification, will be more robust. SMEs may find it helpful to engage patent counsel early to draft “EPC-proof” claim language and fall-back positions (e.g. dependent claims or alternative embodiments) that can be leveraged to clarify scope if needed.

Oppositions and Litigation: G 1/24 has significant implications for post-grant strategies, both in defending patents and challenging others’. For SMEs that own European patents, the decision brings a measure of certainty in how their claims will be interpreted by courts and opponents. Since EPO examiners, opposition divisions, and the UPC are now aligned in always considering the full patent disclosure, an SME patentee can anticipate the scope of protection will be construed consistently across forums.

This reduces the risk of unpleasant surprises in litigation (e.g. a court interpreting a claim more broadly than the EPO did, and finding new prior art that invalidates the patent). It also means that any interpretations or definitions given in the patent itself will likely bind the patentee during enforcement. SMEs should thus be aware that they cannot argue a different scope in court than what a skilled reader would derive from the entire patent document. On the flip side, when SMEs are challenging a competitor’s patent (or defending against one in infringement proceedings), G 1/24 empowers them to exploit the description for their arguments. An opponent in an EPO opposition or a defendant in court can comb through the patent’s description to find broadenings, disclaimers, or specific embodiments that support a certain claim construction favorable to their case. For example, a challenger may point to an explicit description definition to broaden a claim and find previously unconsidered prior art for invalidity, or a defendant might highlight limiting language in the description to argue a narrow claim scope that avoids infringement. Thus, in both offense and defense, SMEs should always analyze a patent as a whole. G 1/24 essentially mandates a holistic interpretative approach, so strategies must account for every statement in the patent, not just the claims in isolation.

In sum, the decision rewards diligent preparatory work (in drafting/prosecution) with stronger patents, and it rewards diligent analysis (in opposition/litigation) by opening additional avenues of argument via the description.

Certainty and Scope of Patent Protection

By harmonizing EPO claim interpretation with that of European courts, G 1/24 contributes significantly to legal certainty in the scope of patent protection. Previously, differences in interpretive approach could lead to misaligned outcomes.

For instance, a patent deemed novel by the EPO might later be invalidated by a national court construing its claims more broadly (or vice versa). Now, with a uniform principle that the description must always illuminate the claims, the risk of such discrepancies is diminished.

Patent scope is determined more predictably: the “extent of protection” conferred (per Article 69 EPC) should correspond to the scope considered during examination and opposition. This coherence benefits SMEs by making the enforcement value of their patents more reliable – a patent granted after thorough description-informed examination is less likely to be undermined by a different interpretation in court. It also provides greater clarity to third parties (including SMEs assessing freedom-to-operate), who can trust that reading a patent’s claims in context is the correct way to understand its boundaries

In essence, G 1/24 reinforces an “eyes-wide-open” approach to patent scope: both patentees and competitors can base their strategies on the full disclosure, leading to a fairer balance between fair protection for patent owners and legal certainty for the public, the very balance the Protocol on Article 69 EPC seeks to achieve!

In Conclusion

The Enlarged Board’s decision in G 1/24 marks a pivotal development in European patent law. It resolves a technical legal question with broad practical ramifications: going forward, no European patent can be divorced from its description when determining what it really claims.

The legal reasoning in G 1/24 is rooted in EPC doctrine and a desire for consistency, rejecting insular claim readings in favor of a contextual approach that mirrors how patents are enforced in the real world.

For SMEs, this decision is a call to action to refine their patent strategies. By drafting applications meticulously, prosecuting them with an eye toward clarity and consistency, and litigating with full awareness of the description’s role, SMEs can better secure and defend their innovations under the European patent system.

In a patent landscape now governed by contextual claim interpretation, those who proactively adapt to these clarified rules will enhance the strength and reliability of their patent rights. G 1/24 thus not only brings doctrinal clarity, but also serves as a valuable guidepost for building robust patent portfolios and litigation positions in Europe.

Ferdinand Leeger MSc