A Practice Note explaining how to appeal a class certification decision under Federal Rule of Civil Procedure (FRCP) 23(f). This Note discusses the reasons for petitioning for permission to appeal under FRCP 23(f), what types of decisions may be appealed, grounds for granting the petition, the parties that can petition for permission to appeal, and when the petition must be filed. This Note also explains how to draft, serve, and file the petition and opposition, and post-petition proceedings.