Sometimes also referred to as file-wrapper estoppel, is a quasi-equitable doctrine of claim construction, which refers to statements made by a patent applicant in order to secure the grant of a patent. Where an applicant says that the scope of claims in a patent is limited in a particular way, that statement will usually bind the applicant with respect to the subsequent patent. The basic principle is that a patentee should not, in litigation, recapture scope for a patent that the patentee had given up during the application (prosecution) process of the patent application.
Classic prosecution history estoppel in U.S. law occurs when a patent applicant make a statement or argument so as to overcome rejection. However, more modern precedents hold that any statement disclamatory of claim scope should be regarded as giving rise to presumption of preclusive effect,” i.e., an estoppel. As a doctrine it is usually described as a limitation on the doctrine of equivalents though in practice disclamatory language in the prosecution history is also applies to claim construction for purposes of literal infringement. See Teach-Away.
The extent to which prosecution history estoppel applies outside US Patent law is more limited. The concept is accepted in Japanese patent law, where the applicant can create an estoppel if it:
- intentionally excludes an embodiment or method from the claims during the prosecution of the patent application,
- acknowledges that an accused embodiment of method is not within the scope of the claims, or
- conducts itself so as to acquiesced in such a limiting interpretation of the scope of its claims.
The situation in Europe with respect to prosecution history estoppel is patchy – and it is fair to characterise many national courts as being jurisprudentially precious and overly fastidious on the issue. Thus:
- the Swedish courts have unambiguously accepted it;
- the French Supreme Court in complex circumlocutions rejected it – while sort of accepting it;
- the English High Court accepted it – but the Court of Appeal issued a puzzling decision which was “obiter dicta” on the issue of estoppel, and deeply unclear as to how file histories should be treated (does estoppel only arise in cases of a lack of antecedent basis (i.e., support for claims in the description);
- the Spanish courts now seem to accept it;
- The German Supreme Court has held that in determining the scope of a patent “occurrences in the examination proceedings which preceded the grant in principle are irrelevant.” – “Es besteht auch kein praktisches Bedürfnis dafür, Vorgängen im Erteilungs- wie im Einspruchsverfahren als solchen, die in der Patentschrift oder in der geänderten Patentschrift keinen Niederschlag gefunden haben, für sich schutzbegrenzende Wirkungen zuzuerkennen.”
The English Court of Appeals decision referenced above, Activis v. Eli Lilly, must be characterised as somewhat difficult to make sense of. The relevant section is:
58. …[I]t assumes that the skilled reader will always read the prosecution history. I do not see why this should be so … Secondly, and more importantly, it suggests that the story told by the prosecution history of how the claims came to be drafted as they were will assist the court in preventing abuse of the system … Unless the acceptance of a restriction in a claim is to operate as some kind of estoppel against the patentee arguing for wider claims (a proposition for which neither side contended and which Jacob J rejected, at least on the basis of domestic estoppel, in Bristol Myers), there will always remain an issue as to whether the applicant needed to accept the restriction notwithstanding that he did so. In those circumstances, the light which the prosecution history sheds on the ultimate question of construction is likely to be extremely limited.
59. I therefore do not regard it as useful to go to the prosecution history in order to discover that the patentee accepted a restriction to his claim against an objection of lack of support in the specification. It is always open to a party attacking the patent to argue that the claims as sought to be construed by the patentee lack support in the specification: see for example American Home Products v Novartis  RPC 8 at . What purpose does it serve to illustrate this point by showing that the patentee was faced with an official objection to that effect and amended his claims in the light of it? It is still open to the patentee to say that he need not have done so, and the apparent concession he made in prosecution was wrongly made. If it is not open to the patentee so to contend, then the prosecution history is indeed creating a form of estoppel.
60. In any event, patent offices are usually concerned with patentability, not scope of protection. If an applicant were to conclude every letter by saying that he did not accept that by accepting this or that limitation he was necessarily restricting the scope of protection, no inference could be drawn from his conduct in accepting it. I would be reluctant to put the patent attorneys’ profession to this unnecessary trouble.
First, any competent intellectual property lawyer, or any skilled reader, at least in the writer’s experience will almost always read the prosecution history, especially if claims are ambiguous or an assertion of infringement is made – especially as both US and European file histories are now readily available online. Second, in the writer’s experience, it is not in the least unusual for a patent applicant to explicitly narrow claims to avoid prior art, a common situation that Lord Floyd here avoids discussing – and indeed the most common form of prosecution history estoppel. Third, the opinion draws a distinction between “patentability” and “scope of protection” that entirely misses the main point of prosecution history estoppel – amendments limiting the scope of protection to avoid claims reading on the prior art are about patentability.
Finally the opinion leaves a problem unaddressed – what about classic prosecution history estoppel – amendments to avoid prior art or unambiguous statements about the scope of the claim language? The decision speaks only to amendments to avoid an objection of lack of support – but the last sentence of paragraph 59 would seem to imply such classic estoppels are accepted.