What does the transitional phrase “comprising” mean in a patent claim?

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.

The transitional phrase “comprising” in a patent claim is inclusive and open-ended. According to the MPEP, The transitional term “comprising”, which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps.

This means that a claim using “comprising” allows for the inclusion of additional elements or steps beyond those explicitly stated in the claim. For example, a claim for a device “comprising A, B, and C” would cover devices that include A, B, and C, as well as devices that include A, B, C, and additional elements.