What is the purpose of a classified search in patent examination?

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 purpose of a classified search in patent examination is to identify the most relevant prior art efficiently. According to MPEP 904.02(a):

“A proper field of search normally includes the subclass in which the claimed subject matter of an application would be classified in the U.S. Patent Classification System and analogous areas of domestic and foreign classification.”

This approach ensures that examiners focus their search efforts on the most likely areas where relevant prior art may be found, based on the subject matter of the application.