The aim of this book is to provide an overview of the roles of amino acids in nutrition and health during the life cycle including the embryo and the adult. Amino acids are not only building blocks for protein synthesis but are also essential precursors for the generation of diverse substances with enormous biological importance in the organism. A detailed overview of amino acids in nutrition and health is presented and new findings about the key roles of amino acids in the prevention and treatment of major health problems in both humans and animals including intrauterine growth retardation, neonatal survival, obesity, diabetes, cardiovascular disease and cancer are discussed.