This is a Phase 3, randomized, double blind, placebo-controlled, three-arm, safety and efficacy study of pirfenidone in patients with idiopathic pulmonary fibrosis. Approximately 400 patients at approximately 70 centers will be randomly assigned (2:2:1) to receive either 2403 milligrams (mg) of pirfenidone, placebo equivalent, or 1197 mg of pirfenidone administered in divided doses three times per day (TID) with food. Patients will be randomized by geographic region.