Can a new category of invention be added in a reissue application?

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, a new category of invention can be added in a reissue application, but it is generally considered broadening the invention. The MPEP states: The addition of process claims as a new category of invention to be claimed in the patent (i.e., where there were no method claims present in the original patent) is generally considered as being a broadening of the invention.

However, there are exceptions to this general rule. For example, if the reissue application adds limitations to a process of making the product claimed in the original patent, it may not be considered broadening. The MPEP provides examples: (1) a process of using the product A (made by the process of the original patent) to make a product B, disclosed but not claimed in the original patent; or (2) a process of using the product A to carry out a process B disclosed but not claimed in the original patent.