This book is designed to serve as a textbook for core as well as elective courses offered to undergraduate and advanced undergraduate students enrolled in chemistry. This textbook comprehensively deals various topics of organic chemistry such as amino acids, peptides, proteins and enzymes. The text is divided into four chapters: a chapter each dedicated to amino acids, peptides, proteins and enzymes, respectively. The important reactions have been explained with the help of the mechanisms involved. It gives a detailed account of the solution phase and solid phase synthesis of peptides as well as discussing the structure and function of some biologically important peptides. It also covers the classification, nomenclature and mode of action of enzymes, and a detailed account of the structure and function of different co-enzymes. The book also includes pedagogical features like end-of-chapter exercises to aid in self learning. Given the scope, this textbook will be useful for graduate and advanced graduate students pursuing the course of chemistry, especially organic chemistry.