A Practice Note discussing ex parte expungement and reexamination proceedings in the United States Patent and Trademark Office (USPTO) seeking cancellation of federal trademark registrations for marks that have not been used in commerce as required by the Lanham Act. It discusses which registrations are subject to expungement and reexamination, what a third party must do and show to successfully petition the USPTO Director to initiate a proceeding, and what a registrant must show to prove use of its mark and defend against a proceeding.