When can prior art or Section 301 written statements be filed for a patent?

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.

Prior art or Section 301 written statements can be filed “at any time during the period of enforceability of a patent.” As stated in MPEP 2204:

“Submissions may be filed ‘at any time’ under 35 U.S.C. 301. However, this period has been defined by rule (37 CFR 1.501(a)) to be ‘any time during the period of enforceability of a patent.’”

This period typically includes the term of the patent plus six years, accounting for the statute of limitations for infringement actions.