Melatonin is a natural hormone originating from the pineal gland. It has a circadian secretion pattern with highest concentrations during the night. Intense research during the past 20-30 years has revealed that when melatonin is given in supra-physiologic doses, i.e. as tablets in milligram doses, it has a number of very important effects. Thus, melatonin can be used for various sleep disorders including insomnia, and circadian disturbances such as shiftwork and jetlag. Melatonin is the strongest known antioxidant drug with effects in cardiac disease, cancer, depression, brain damage such as dementia and Alzheimer's disease, and the immune system. This book describes all these mechanisms of melatonin and discusses the potential beneficial effects in diseases of the heart, brain, cancer, and diabetes. Melatonin also has strong effects against sunburn and sun-induced skin cancers, with potential strong effects against skin aging, and animal studies have shown a clear life-prolonging effect. Finally, melatonin can be used in warfare against nuclear disasters and sulfur mustard. The amazing thing about this drug is that it is cheap, it does not induce tolerance or dependency, and it is non-toxic even in extremely high doses. The authors, professor Ismail Gogenur and professor Jacob Rosenberg, are well known scientists within the effects of melatonin on various organ functions. They have studied the effects of melatonin in different clinical scenarios for the past decade and have mentored several PhD theses in this clinical field. They are based in Copenhagen, Denmark, with research collaborators all over the world."