What makes a claim indefinite under 35 U.S.C. 112(b)?

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.

A claim can be considered indefinite under 35 U.S.C. 112(b) if it creates confusion about when direct infringement occurs. The MPEP 2173.05(p) provides an example from the In re Katz case:

“A single claim which claims both an apparatus and the method steps of using the apparatus is indefinite under 35 U.S.C. 112(b) or pre-AIA 35 U.S.C. 112, second paragraph.”

For instance, a claim that includes both system elements and user actions can be indefinite because it’s unclear whether infringement occurs when the system is created or when a user performs certain actions. To avoid indefiniteness, claims should focus on the capabilities of the system rather than specific user actions.