Noninvasive mechanical ventilatory techniques include the use of negative and positive pressure ventilators. Negative pressure ventilators support ventilation by exposing the surface of the chest wall to subatmospheric pressure during inspiration, whereas expiration occurs when the pressure around the chest wall increases and becomes equal to or greater than atmospheric pressure. In this article, a description of negative pressure ventilators and the physiologic effects of negative pressure ventilation (NPV) is given, and the application of this technique in the long-term treatment of chronic respiratory failure is summarized. Many studies, although uncontrolled, have shown that long-term treatment with NPV can improve respiratory muscle function, arterial blood gases, and survival in patients with neuromuscular and chest wall disorders. NPV devices, however, are more cumbersome and difficult to use than home positive pressure ventilators (PPVs) and tend to predispose to obstructive apnoeas during sleep. In the last several decades, NPV has been supplanted by mask PPV. In experienced hands, NPV remains a second viable option in patients with neuromuscular and chest wall disorders who, for technical or other reasons, cannot be offered mask PPV. There is no evidence, however, that long-term treatment with NPV can improve respiratory muscle function, exercise endurance, quality of life, and survival in patients with severe chronic obstructive pulmonary disease.