The aim of this theme is to highlight the important points related to melatonin. It is a hormone secreted in pineal glands and helps in the induction of sleep in human beings. Melatonin is a naturally occurring compound in animals, plants and microbes. It is responsible for the regulation of circadian rhythms for several biological functions. It is sensitive to the light and its concentration in the milk varies with the intensity of light. The basic functions of this hormone include antioxidant property, in correction of sleeping disorders, in alleviation of jet lag and in prevention of cancers. Besides these major functions, it also has some associated functions like protection of skin damage from ultraviolet light. Generally, <0.3 mg melatonin is required per day for human beings for usual induction of sleep and relaxation.