Nasal CPAP has become the treatment of choice for obstructive sleep apnea because of its predictable physiologic effect over the full spectrum of disease. The physiology of the upper airway during sleep mimics the behavior of a collapsible tube; CPAP prevents the negative intraluminal pressure thought to cause apnea, hypopnia and increases in airway resistance. Titration of CPAP for optimal therapy is not well standardized. However, treatment algorithms should aim to eliminate apneas, hypopneas, snoring, significant O2 desaturations, and EEG arousals. Flow limitation (recognized from the shape of the flow tracing) may also need to be eliminated. Once prescribed, CPAP is effective but compliance with therapy is not uniform or optimal. Attention to details of comfort and various enhancements to CPAP may improve results but need to be validated. Automatically adjusting CPAP may provide a new therapeutic option, but again needs to be carefully evaluated to define improvements possible in ease of titration, effectiveness, and ultimate compliance.