Amino acids are molecules with both an amino group and carboxylic group. There are 20 kinds of naturally occurring amino acids with optical active structures at α-position (L-amino acids) except glycine. Greenstein and Winitz said: “Few products of natural origin are versatile in their behavior and properties as are the amino acids, and few have such a variety of biological duties to perform” in their preface of Chemistry of the Amino Acid in 1961.1 Subsequently signicant progress has been made on the knowledge of amino acids, and technical achievements to utilize such progress are remarkable, including cosmetic and cosmeceutical applications. This is due to the market growth and cost reduction of certain amino acids for many industrial applications. For example, in food applications there is huge and still growing consumption generated for glutamic acid (Glu) and glycine (Gly) as food additives and aspartic acid (Asp) and phenylalanine (Phe) as raw materials for the articial sweetener “aspartame.” Consumption of lysine (Lys), methionine (Met), and threonine (Thr) is expanding in the animal food additives market. Cysteine (CysH) and proline (Pro) are major amino acids utilized in the avor industry to manufacture natural avors by Maillard reaction with sugars. Health food and pharmaceutical intermediates are other rapidly growing markets for many amino acids. In this chapter, the role of amino acids and derivatives are reviewed as functional molecules for cosmeceutical applications.