The optimal ablation approach for patients with persistent atrial fibrillation (AF) remains unknown. In particular, it is unclear if pulmonary vein (PV) antral isolation (PVI) is sufficient as a lone strategy for persistent AF. Furthermore, if additional substrate ablation is to be added, the ideal approach to substrate ablation is yet to be determined.The aim of this study is to determine the optimal strategy of catheter ablation of persistent AF by comparing the efficacy of 3 strategies: PVI vs PVI plus complex fractionated electrogram (CFE) ablation (PVI + CFE) vs PVI plus linear ablation (PVI + Lines).The STAR AF II study (ClinicalTrials.gov NCT01203748) is a prospective, multicenter, randomized trial with a blinded assessment of outcomes. A total of 549 patients will be randomized in a 1:4:4 fashion to one of the investigation arms: PVI, PVI + CFE, and PVI + Lines, respectively. Patients undergoing a first-time ablation procedure for symptomatic, persistent AF that is refractory to at least 1 antiarrhythmic medication will be included. Persistent AF will be defined as a sustained episode lasting>7 days and=60 mm will be excluded. The primary end point is freedom from documented AF>30 seconds at 18 months after 1 or 2 ablation procedures with or without antiarrhythmic medications.The STAR AF II study is a randomized trial designed to evaluate the optimal approach for catheter ablation of persistent AF.