This is a multicenter, double-blind, parallel, placebo-controlled, randomized phase 2 study to evaluate the safety and efficacy of Gleevec (imatinib mesylate) in the treatment of Idiopathic Pulmonary Fibrosis (IPF). One-hundred- twenty patients will be enrolled in the trial in total. Subjects must have a diagnosis made by HRCT showing definite or probable IPF and clinical symptoms consistent with IPF with onset between 3 and 36 months prior to screening. Subjects will be randomly assigned to receive either Gleevec 600 mg orally or placebo, once per day for approximately 2 years. The primary efficacy will be progression defined as a greater than 10% decline in the forced vital capacity or death. Measures of safety will include all randomized patients who receive at least one dose of study medication. All adverse events and serious adverse events will be separately tabulated and mapped to a standard classification system and grouped by body system. Any serious adverse events that occur during the trial and 30 days after the end of therapy will be reported to the FDA within 24 hours and followed to outcome.