 In the trial, the investigators will test the following hypotheses: 1 People with ALS who have a FVC greater than 50 percent can tolerate active NIPPV and control NIPPV, and will find control NIPPV to be a believable treatment; 2 Initiation of active NIPPV in people with ALS who have a FVC greater than 50 percent will have better clinical outcomes with respect to measures of quality of life, rate of pulmonary function decline, and functional outcome; and 3 People with ALS who start active NIPPV early will have improved tolerance later when respiratory weakness has progressed. These aims will enable planning of a subsequent, large-scale and definitive clinical trial of early NIPPV FVC greater than 50 percent in people with ALS. 