Leucine is a branched-chain essential amino acid. It accounts for approximately one-fifth of the requirements for essential amino acids. Leucine facilitates insulin-stimulated glucose uptake and insulin signalling in skeletal muscle cells. This book includes chapters on the physiological roles of leucine and the effects of leucine supplementation; the syntheses, properties and applications of the main leucine containing polymers and materials made of them that up to now have been studied; and the effects of hydroxy- beta methylbutyrate (HMB) and alpha-ketoisocaproate (KIC), which are metabolites of leucine on muscle function and sports performance based on recent findings.