In the past decade, an increasing number of publications on the sleep-modulatory activities of various kinds of endogenous peptides has appeared. Thus, it is currently necessary to reassess the overall knowledge available on this subject. This is the first monograph to cover important aspects of studies on "sleep peptides." It contains seven review articles with full literature surveys. Both basic and clinical aspects are dealt with comprehensively. Professional sleep researchers and neuroscientists in various research disciplines reconstruct the classical concepts of the function and regulatory mechanisms of sleep through the impact of up-to-date findings on endogenous sleep-modulators.