This review article shows the potential of lung ultrasound in the critically ill (LUCI) to study lung sliding and describes the optimal equipment for its assessment. Then, it analyses the integration of lung sliding within lung ultrasound then whole body critical ultrasound. It describes the place of lung sliding in the BLUE-protocol (bedside lung ultrasound in emergency) (lung and venous ultrasound for diagnosing acute respiratory failure), the FALLS-protocol (fluid administration limited by lung sonography) (the role of lung sliding in circulatory failure), and the SESAME-protocol (sequential assessment of sonography assessing mechanism or origin of severe shock of indistinct cause) (whole body ultrasound in cardiac arrest). In the LUCIFLR project (LUCI favoring limitation of radiations), the consideration of lung sliding allows drastic reduction in irradiation and costs. In conclusion, lung sliding is proposed as a gold standard for indicating the presence of the lung at the chest wall and its correct expansion.