This is a Phase 3, randomized, double-blind, placebo-controlled, safety and efficacy study of pirfenidone in patients with idiopathic pulmonary fibrosis (IPF). Approximately 320 patients at approximately 50 centers will be randomly assigned (1:1) to receive pirfenidone 2403 milligrams or placebo equivalent administered in divided doses three times per day (TID) with food. The primary outcome variable will be the absolute change in percent predicted Forced Vital Capacity from Baseline to Week 72. Patients will be randomized by geographic region.