What is the difference between essential and nonessential material 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.

In patent applications, the distinction between essential and nonessential material is important for incorporation by reference:

• Essential material is defined in 37 CFR 1.57(d) as material necessary to meet the requirements of 35 U.S.C. 112(a), (b), or (f). It can only be incorporated by reference to a U.S. patent or U.S. patent application publication.
• Nonessential material is subject matter referred to for purposes of indicating the background of the invention or illustrating the state of the art. It can be incorporated by reference to a wider range of sources, including foreign patents and non-patent publications.

As stated in the MPEP: ‘Other material (‘Nonessential material’) may be incorporated by reference to U.S. patents, U.S. patent application publications, foreign patents, foreign published applications, prior and concurrently filed commonly owned U.S. applications, or non-patent publications.’