Prosecution history estoppel comes to Canada

The December 2018 Royal Assent of Bill C-861 introduced new section 53.1 to the Patent Act, which brought prosecution history estoppel to Canada. This amendment removes the bar on the use of prosecution history during subsequent litigation, that has endured since the Supreme Court of Canada’s 2000 judgment in Free World Trust.2 While the impact of the prosecution history of a patent has long been a point of consideration in respect of U.S. proceedings, this amendment introduces a new element to patent prosecution and litigation in Canada.

What you need to know

  • Patent prosecution history is admissible into any action or proceedings that was not finally disposed of as of December 13, 2018.3
  • Under the new law, certain written communications between the applicant or patentee and the Commissioner or Patent Office may be admitted into evidence during claim construction in subsequent proceedings regarding the patent. The communications are only admissible to rebut representations made by the patentee in the proceedings.
  • Applicants and patentees will need to be mindful of written statements made to the Canadian Intellectual Property Office (CIPO) during prosecution of a patent application and during post-grant procedure such as disclaiming, re-issuing or re-examining an issued patent, as the patentee may be held to those representations in subsequent Canadian ligation, thereby limiting a patentee’s litigation strategy options. Applicants and patentees will want to work closely with their patent counsel when preparing written submissions to CIPO.
  • By virtue of the admissibility of prosecution history, it will be challenging to reclaim ground that was disclaimed during prosecution in subsequent litigation.
  • For those challenging patents in litigation or assessing freedom to operate, the prosecution history will be a useful source of information for litigation strategy and to manage expectations regarding claim construction.

Prosecution history estoppel

At common law, the prosecution history of a patent has been inadmissible in subsequent, related proceedings in Canada.4 This inapplicability of the doctrine of prosecution history estoppel has long been a notable difference between Canadian and American patent law. File wrapper estoppel (as it is known in the U.S.), under which the prosecution history is admissible in subsequent proceedings and the applicant is bound by such evidenced statements, has long existed in the United States.5

With the enactment of section 53.1 of the Patent Act, certain written communications between the applicant or patentee and the Commissioner or member of the Patent Office, will now be admissible into evidence in actions or proceedings regarding the patent.6 The provision permits such evidence to be used to rebut representations made by the patentee in claim construction, if the communications were prepared in regards to prosecution of the patent application, disclaimers, or any re-examination request or proceeding. For divisional applications, the prosecution history of the original application will also be admissible into evidence. Similarly, for reissued patents, the prosecution history of the surrendered patent and application for reissuance are considered communications in respect of prosecution of the patent.

What’s next

It remains to be seen how the Federal Courts will apply this new provision. The use of patent prosecution histories during claim construction in U.S. and U.K. litigation should provide early guidance, as the body of Canadian case law develops. In any case, Canadian practitioners should be mindful of statements that are made during prosecution in view of the change in law.


1 Bill C-86, Budget Implementation Act, 2018, No. 2, 1nd Sess, 42nd Parl, 2018 [Bill C-86].

2 2000 SCC 66.

3 Bill C-86, Budget Implementation Act, 2018, No. 2, 1nd Sess, 42nd Parl, 2018, s. 203(1).

4 Free World Trust v Électro Santé Inc., 2000 SCC 66 at paras 61-67.

5 Graham v John Deere, 383 US 1 (1966).

6 Patent Act, RSC 1985, c P-4, s. 53.1.

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This publication is a general discussion of certain legal and related developments and should not be relied upon as legal advice. If you require legal advice, we would be pleased to discuss the issues in this publication with you, in the context of your particular circumstances.

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