Exploration of the lung, a vital organ, is clinical, but is supplemented in practice by radiography or CT scan. These methods have their drawbacks and this update will review the possibilities of a method that provides an accurate picture of the respiratory status, in bed, in a critical patient: pulmonary ultrasound. Using a standardized semiology, ultrasound offers the possibility to diagnose pleural effusion, pneumothorax, alveolar consolidation and interstitial syndrome with likelihood ratios close to CT. In addition to the interventional part, a basic application is codified in the patient in acute respiratory distress, which allows an immediate diagnosis, and the possibility of reducing the use of the thoracic scanner.