File Wrapper Estoppel In Canada

The Canadian Patent Act was amended last year to include a new provision which allows prosecution histories into evidence in patent proceedings to rebut representations made by the patentee regarding claims construction.

This amendment overturned the longstanding principle in Canadian patent law that claims are to be construed without regard to extrinsic evidence, including statements made during prosecution. This amendment may result in the adoption of file wrapper estoppel or a similar rule of claims construction in Canada; however, its application remains subject to judicial interpretation.

The History of File Wrapper Evidence in Canada

In the U.S., patent prosecution histories (also known as "file wrappers") are regularly considered in the claims construction analysis, where the principle known as prosecution history estoppel (or file wrapper estoppel) precludes patentees from asserting a position regarding claims construction during litigation that is inconsistent with the patentee's statements made to the USPTO during prosecution. For example, where an applicant makes representations during prosecution that...