A Practice Note addressing US Patent and Trademark Office (USPTO) ex parte reexamination and supplemental examination proceedings. This Note discusses key features, procedural and substantive requirements, and strategic considerations for filing and prosecuting a patent owner or third-party ex parte reexamination request based on prior art patents and printed publications, including the substantial new question of patentability (SNQ) threshold standard the USPTO applies for instituting reexamination. This Note also discusses patent-owner-requested supplemental examination, including its inequitable conduct safe harbor provision, and ex parte reexamination ordered after an SNQ determination.