This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides a synthesis of the diverse of research that has been carried out on the reproductive biology of crustaceans and aims to emphasise as case studies current active research on lobsters and shrimps. It explores the most important aspects of crustacean reproduction in relation to their exploitation by fisheries. The book examines the list of maturity indicators and their respective relationships to body size and maturity for different species of crustaceans around the world for both males and females. It reviews the different aspects of sexual selection and demonstrates the diversity of mating behaviour and mating systems in Crustacea. The book focuses on research on the hormonal control of vitellogenesis and ovarian maturation. It shows that the endocrine regulation of both reproduction and molting is controlled by a complex interaction of neuropeptides, juvenoids and steroids.