Since its first description in 1967, a lot of progress has been made in understanding the pathophysiology, diagnosis and management of acute respiratory distress syndrome (ARDS). This nosological entity is based on the appearance of a diffuse alveolar damage associating pulmonary epithelial barrier disruption with an alveolar filling, both responsible of profound hypoxemia and important morbi-mortality. Nowadays, ARDS remains a frequent syndrome, associated with various etiologies. Diagnosis is based on the occurrence of acute hypoxic respiratory failure not explained by cardiac insufficiency or volume overload, within 7 days after a recognized risk factor, and in the presence of bilateral pulmonary opacities not fully explained by effusions, atelectasis or nodules on the chest radiography. Survivors present an increased risk of developing cognitive decline, depression, post-traumatic stress, and typical ICU related side-effects such as polyneuropathy and sarcopenia. In this context and not withstanding significant recent progress in the field of mechanical ventilation and extra-corporeal respiratory assistance, early diagnosis remains essential to identify patients with ARDS in order to offer them the most appropriate therapy.