The organic compounds which contain a side chain (R group), along with carboxyl (-COOH) and amine (-NH2) functional groups, are known as amino acids. They are the structural units that combine to form proteins. Hydrogen, carbon, oxygen and nitrogen are key elements of an amino acid. The set of metabolic pathways through which amino acids are produced is known as amino acid synthesis. Essential amino acids are the amino acids that cannot be synthesized by the body of an organism and are therefore supplied through diet. Other important types include proteinogenic amino acids, non-proteinogenic amino acids, non-standard amino acids, etc. Due to its biological importance, they are widely used in nutrition and are often used in food technology, fertilizers, animal feeds, nutritional supplements, etc. The book aims to shed light on some of the unexplored aspects of amino acids. Such selected concepts that redefine the subject have been presented herein. This book will provide comprehensive knowledge to the readers.