A rich and complexly interwoven matrix of psychosocial and physiological variables influence those transformations of consciousness that we label sexual. Much more than for other "instinctive" behaviors, sexual activity manifestly involves a set of unique physiological correlates, interacting with a highly prized array of subjective experiences. The physiological, behavioral, and experiential events undergo slow shifts of intensity and quality as well as sharp transformations from one 'state" to another. Furthermore, this is a realm of human experience directly accessible to all and obviously essential to the preservation of the species. For these reasons, sexual phenomena are of great potential interest to students of psychophysiology and can provide unique and important models for psychobiological research.