Creatine is an organic acid that contributes to the energy supply to the skeletal muscle. The basic substrates for creatine biosynthesis in the human body are semi-essential amino acids L-arginine, glycine and methionine. In this book, the authors discuss the biosynthesis, therapeutic uses and physiological effects of creatine supplementation. Topics include the role of creatine in the pathophysiology of depression and the possible mechanisms underlying its antidepressant effect; creatine treatment and positive effects on muscle performance, muscle mass gain, and the persistence and improvement of the quality of life in patients with chronic diseases; muscle ergogenic effects of creatine supplementation in resistance exercise training; experimental evidence that creatine supplementation during pregnancy is protective for the neonate; and creatine metabolism and role in sports physiology.