How are Inter Partes Reexamination Certificates numbered?

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.

Inter Partes Reexamination Certificates are numbered using a specific system. According to MPEP 2690:

“The inter partes reexamination certificates will be numbered in a separate and new ordinal sequence, beginning with “(1st)”. The certificate number will always be the patent number of the original patent followed by a two-character “kind code” suffix. The “kind code” suffix is C1 for a first reexamination certificate, C2 for a second reexamination certificate for the same patent, etc.”

This numbering system allows for easy identification of the reexamination history of a patent.