Idiopathic pulmonary fibrosis (IPF), synonymous with cryptogenic fibrosing alveolitis (CFA), is a progressive and usually fatal disease of unknown cause characterized by sequential acute lung injury with subsequent scarring and end-stage lung disease. Historically, IPF/CFA encompassed a heterogeneous group of different histological and clinical entities arising in an idiopathic setting. Recently, the American Thoracic Society (ATS) and European Respiratory Society (ERS) core committee has redefined diagnostic criteria for both IPF/CFAand idiopathic interstitial pneumonias confining the term IPF/CFA to patients with a histological pattern of usual interstitial pneumonia on lung biopsy. This review attempts to refine the clinico-radiological-pathological features that together define IPF/CFA as it is understood today, and to summarize the rationale of new therapeutic approaches based on the current understanding of the pathogenetic mechanisms.