Noninvasive ventilation (NIV) refers to the delivery of mechanical ventilation using a nasal or facial mask. Compared to mechanical ventilation with endotracheal intubation, the occurence of complications, mainly infectious, is reduced by NIV. Reduction of respiratory workload and improvement of gas exchange are achieved with the use of NIV. In patients with exacerbations of chronic obstructive pulmonary disease (COPD), NIV reduces the need for endotracheal intubation, the length of ICU stay and the mortality. It is equally effective in acute cardiogenic pulmonary edema and for ventilatory weaning of patients with COPD. In selected groups of patients with acute hypoxemic respiratory failure, NIV diminishes the rate of endotracheal intubation and improves survival. The purpose of this article is to review the mechanisms, the technical aspects and the indications of NIV for the treatment of acute respiratory failure.