This book describes the reproductive strategies and tactics employed by bivalve and gastropod molluscs to exploit and take advantage of different environments, and their response to different environmental fluctuations. The first chapter gives a general overview of the reproductive strategies and tactics developed through time as a means of adapting to different environments, including: morphological variations, reserve storage strategies; gametogenic effort, duration and intensity; storage of gametes, duration and intensity of spawn and post spawn; and the need and duration of a rest or recovery period. Chapters two and three give an up-to-date overview of histological oogenesis and spermatogenesis, pointing out the variation in morphology and gametogenic processes. Chapters four and five present the different tactics adopted by different species and populations of the same species to various environments, demonstrating the plasticity of mollusc reproduction capacities, which permits them to use different environments and to thrive in changing environments.