What is a C-STAR (C*) in CPC classification?

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.

A C-STAR (C*) is an important designation in the Cooperative Patent Classification (CPC) system. According to MPEP 905.03(a):

“A C-STAR (C*) is applied to an allocated symbol from the classification picture on an application when that symbol represents at least one concept that is claimed.”

Key points about C-STAR:

• It is mandatory to apply C* designations.
• C* applies to symbols representing claimed concepts, regardless of type or position.
• No new CPC symbols should be allocated solely for C* purposes.
• Narrow/specific CPC symbols falling within claimed subject matter should be designated as C*.
• At least one CPC symbol must be designated as a C*, but there’s no upper limit.

C-STAR helps identify which parts of the classification picture directly relate to the claimed subject matter, enhancing search precision.