Melatonin is a hormone that is associated with the control of sleep-wake cycle and is primarily secreted by the pineal gland at night. It is also taken orally as a dietary supplement to treat short-term insomnia such as from shift work or jet lag. Some melatonin receptor agonists are also available as medications that work as melatonin but may have some adverse effects for sleep conditions. Side-effects of melatonin use are headaches, somnolence, diarrhea, nausea, nervousness, irritability, abnormal dreams, psychomotor hypersensitivity, mouth ulcers, chest pain, mood swings, etc. These side-effects are minimal if taken at a low concentration for short durations. It is also involved in synchronizing circadian rhythms. This book provides significant information of this discipline to help develop a good understanding of the clinical perspectives of melatonin as well as its pharmaceutical applications. It unravels the recent studies in this field. This book will serve as a valuable source of reference for graduate and post graduate students.