How does the USPTO determine if species are patentably distinct?

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 USPTO determines if species are patentably distinct by evaluating their unique characteristics and inventive features. According to MPEP 806.04:

“Species are patentably distinct if they are mutually exclusive (i.e., there is no embodiment that would infringe both claims) and if there would be a serious burden on the examiner if restriction is not required.”

To be considered patentably distinct, species must have materially different designs, modes of operation, or effects. The examiner assesses whether searching for one species would likely uncover art relevant to the other species, and whether separate classification or different field of search is required for each species.