Prosecution history estoppel

Prosecution history estoppel, also known as file-wrapper estoppel, is a term used to indicate that a person who has filed a patent application, and then makes narrowing amendments to the application to accommodate the patent law, may be precluded from invoking the doctrine of equivalents to broaden the scope of their claims to cover subject matter ceded by the amendments. Although primarily a U.S. term, questions of whether, or the extent to which the prosecution history should be relevant for determining the extent of protection of a patent also arise outside the U.S.

Patents in Canada are subject to a purposive construction, which relies on reading both the claims and the specifications to determine the scope of a patent, and extrinsic evidence is not permitted. Therefore, the Canadian courts emphatically reject what they refer to as "file wrapper estoppel". No distinction is drawn between cases involving allegations of literal infringement and those involving substantive infringement, which means that the negotiations that have taken place between the patentee and the Patent Office cannot be used in order to establish a particular equivalent. Similarly, a patentee is barred from using any previous negotiations with the Patent Office in order to determine the scope of the claims of the patent (i.e. the negotiations cannot be used by the patentee or against the patentee in determining the scope of the claims within the patent).

This is one of the significant differences that exist between Canadian and US patent jurisprudence, which leads some legal commentators to state that Canada is more friendly for rights holders in pursuing patent claims.

The German Supreme Court, the Bundesgerichtshof, ruled in 2002 that "For the determination of the extent of protection of a patent, occurrences in the examination proceedings which preceded the grant in principle are irrelevant".

The Irish Supreme Court has ruled that "evidence from the file which reflects the views of the patentee as to the construction of the claims is inadmissible".

The Dutch Supreme Court has effectively come to the opposite conclusion to most other countries in Europe. The Dutch Supreme Court has stated that where "a third party invokes the examination file in the course of confirming the interpretation defended by him of a patent, it cannot be seen that that requirement [the reasonable doubt threshold] would force any restriction on involving public data from the examination file with the interpretation of the patent".

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Wikipedia