Noninvasive mechanical ventilation refers to the delivery of mechanical ventilatory assistance without the need for an invasive airway. Numerous forms of noninvasive ventilation have been used over the past century, including negative-pressure ventilators, rocking beds, and pneumobelts. For reasons of enhanced convenience and effectiveness, however, noninvasive positive-pressure ventilation (NPPV) has become the predominant form of noninvasive ventilation worldwide. Both in the chronic setting to treat chronic respiratory failure caused by restrictive thoracic diseases and, more recently, in the acute setting to treat conditions such as chronic obstructive pulmonary disease (COPD) exacerbations and acute cardiogenic pulmonary edema, NPPV has gained wide acceptance. Less attention has been paid to applications in the post acute setting, but noninvasive ventilation clearly has a role to play in this setting. The following article discusses the rationale for use of noninvasive ventilation, briefly reviews applications in the acute and chronic settings, discusses appropriate applications in the post acute setting, and describes techniques of application.