Non-invasive ventilation is a technique to ventilate patients without endotracheal intubation and analgosedation. Pressure tight masks allow the ventilation of patients with severe respiratory or ventilatory insufficiency. Non-invasive ventilation may be used as short-term treatment for patients with acute ventilatory decompensation, as well as for long-term therapy at home for patients with chronic respiratory diseases. The typical indications are hypoxaemic respiratory failure in pneumonia or cardiogenic pulmonary edema, and hypercapnic ventilatory insufficiency in severe chronic obstructive pulmonary disease, neuromuscular disorders, or advanced kyphoscoliosis. The physiological background, technical aspects of performing non-invasive ventilation, and typical indications are discussed.