The pineal gland is an enigma within the central nervous system that appears to exert tremendous control over the homeostatic mechanisms of the body. In the animal kingdom, the pineal gland and the hormone it produces, melatonin, regulate circadian rhythms, sleep-wake cycles, thermal and immunologic systems, and reproductive capability. Human research has demonstrated that the pineal gland also plays a role in sleep disturbances, menstrual and reproductive irregularities, psychological and behavioral disorders, and may even serve as a tumor inhibitory gland. Although research is still in the early stages, it is apparent that the pineal gland and melatonin have widespread effects and optimal functioning of the pineal gland is essential to our well-being.