Ultrasound of the diaphragm is an emerging technique that is performed at the bedside and allows assessment of diaphragm function in a variety of settings. Ultrasound is widely available, can be repeated if necessary, and is non-irradiating. First developed in intensive care, mainly for weaning from mechanical ventilation, its use is now extending to pulmonology. Different measurements are described such as diaphragmatic excursion, diaphragmatic thickness and diaphragmatic thickening fraction. The latter helps to diagnose dysfunction and is correlated with pulmonary hyperinflation. The main use in pulmonology is for the respiratory evaluation of patients with neuromuscular diseases, for the search of isolated diaphragmatic impairment and for patients with COPD. Numerous studies are in progress to better determine the role of diaphragmatic ultrasound.