Lung ultrasound has proven to be useful in detecting pneumothorax, interstitial syndrome, and lung consolidation. It is easily applied at the bedside, in real-time, and free of radiation hazards. Recently, the use of lung ultrasound has moved from a diagnostic tool to a monitoring tool for lung aeration quantification. This article reviewed the use of lung ultrasound in monitoring acute pulmonary edema, acute respiratory distress syndrome, and pneumonia, and how it could be used to monitor changes during the application of mechanical ventilation or other treatments for respiratory failure.