What are the most common grounds for rejection in patent applications?

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 most frequent grounds for rejection in patent applications are based on prior art. As stated in the MPEP, By far the most frequent ground of rejection is on the ground of unpatentability in view of the prior art, that is, that the claimed subject matter is either not novel under 35 U.S.C. 102, or else it is obvious under 35 U.S.C. 103. This means that patent examiners most often reject claims because they find that the invention is either not new or is an obvious variation of existing technology.