This book discusses recent advances in theoretical–computational studies on the biosynthesis of melanin pigment (melanogenesis). These advances are being driven by the development of high-performance computers, new experimental findings, and extensive work on medical applications involving the control of pigmentation and the treatment of challenging dermatological diseases. Understanding the elementary processes involved in chemical reactions at the atomic scale is important in biochemical reaction design for effective control of the pigmentary system. Accordingly, the book focuses on the elementary steps involved in melanogenesis, which crucially affect the composition of the resulting melanin pigment by means of competitive reactions. The book also addresses reactions analogous to melanogenesis, with a focus on o-quinone reactions, which are especially important for understanding melanogenesis-associated cytotoxicity.