What is the difference between ex parte and inter partes reexamination?

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.

While MPEP § 2695 doesn’t directly define the difference between ex parte and inter partes reexamination, it mentions both types in the context of reexamination of a reexamination:

“…regardless of whether the reexamination certificate was issued for an ex parte reexamination or an inter partes reexamination, and regardless of whether the pending reexamination proceeding is an ex parte reexamination or an inter partes reexamination.”

The key difference is that ex parte reexamination involves only the patent owner and the USPTO, while inter partes reexamination (which is no longer available but may still be relevant for some patents) allowed third-party participation throughout the process. However, for the purposes of processing a reexamination of a reexamination, these distinctions do not affect the procedure.