The lung is classically investigated using physical examination and radiographs and computer tomography (CT) scans complement this approach. These traditional tools do, however, have drawbacks. The present article shows the potential of an immediate and accurate method of investigating this vital organ: lung ultrasound. Ten signs allow the precise location of the lung (bat sign), the definition of a normal lung surface (lung sliding, A-lines), pleural effusion (quad sign, sinusoid sign), lung consolidation (tissue-like sign, shred sign), interstitial syndrome (lung rockets) and pneumothorax (stratosphere sign, lung point). A simple grey-scale unit and a particular probe - microconvex, ideal for the lung, but also for the whole body in the critically ill - are required. Using these standardized signs, lung ultrasound allows main acute disorders to be diagnosed with an accuracy close to that of CT. With regards to the interstitial syndrome, although traditionally not used by the intensivist (using ultrasound or any other method), this application provides a standardized approach in two basic settings: acute respiratory failure (BLUE-protocol) and acute circulatory failure (FALLS-protocol). The ten signs assessed in the adult can also be applied in the neonate, since no differences are found. In most other settings (Acute Respiratory Distress Syndrome, trauma, pulmonology, cardiology), the same ten signs are the basis. Interventional ultrasound is of major help in the critically ill. Although neglected since the birth of ultrasound, the lung is fully accessible by this method. The main outcomes of this visual approach are an immediate bedside diagnosis and the possibility of decreasing procedures involving radiation exposure. © 2012, Nederlandse Vereniging voor Intensive Care. All Rights Reserved.