Idiopathic interstitial pneumonias represent a group of complex lung diseases among which the most frequent types are idiopathic pulmonary fibrosis (IPF), idiopathic non-specific interstitial pneumonia (idiopathic NSIP), and cryptogenic organizing pneumonia (COP). Clinicians may rely on a precise classification of these diseases from an America-European consensus that has been published in 2002. However it appears that diagnosis should always be confirmed by a multidisciplinary team discussion with experience in the field. There are generally tremendous prognostic and therapeutic implications for the patient.