Can extrinsic evidence be used to interpret patent claim terms?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Yes, extrinsic evidence can be used to interpret patent claim terms, but it is generally considered less significant than intrinsic evidence. The MPEP 2111.01 provides guidance on this matter:

“Extrinsic evidence may be used to interpret claims if the intrinsic evidence does not establish the meaning of a claim term and may also be useful for demonstrating how a disputed term is used by those skilled in the art.”

However, it’s important to note that extrinsic evidence should not be used to contradict the clear meaning of terms in the patent claims as understood from the intrinsic evidence. Intrinsic evidence, which includes the patent specification, claims, and prosecution history, is given priority in claim interpretation.