The primary objectives of the proposed experimental and modeling efforts are to quantify the influences of acute sleep deprivation (short-term homeostatic), chronic sleep restriction (long-term homeostatic), circadian rhythmicity, and their interactions on neurocognitive performance and to develop a new model of sleep homeostasis that can predict the effects of chronic sleep restriction. This model will be based on the underlying neuroanatomy and neurophysiology. This new model will facilitate optimization of human performance in operational settings, such as are seen in military operation and other work environments.