Noninvasive ventilation (NIV), the provision of ventilatory assistance without an artificial airway, has emerged as an important ventilatory modality in critical care. This has been fueled by evidence demonstrating improved outcomes in patients with respiratory failure due to COPD exacerbations, acute cardiogenic pulmonary edema, or immunocompromised states, and when NIV is used to facilitate extubation in COPD patients with failed spontaneous breathing trials. Numerous other applications are supported by weaker evidence. A trial of NIV is justified in patients with acute respiratory failure due to asthma exacerbations and postoperative states, extubation failure, hypoxemic respiratory failure, or a do-not-intubate status. Patients must be carefully selected according to available guidelines and clinical judgment, taking into account risk factors for NIV failure. Patients begun on NIV should be monitored closely in an ICU or other suitable setting until adequately stabilized, paying attention not only to vital signs and gas exchange, but also to comfort and tolerance. Patients not having a favorable initial response to NIV should be considered for intubation without delay. NIV is currently used in only a select minority of patients with acute respiratory failure, but with technical advances and new evidence on its proper application, this role is likely to further expand.