The fascination of the Annelida to scientists lies in the beauty of their structures and the functionality of their body plan, the tremendous adaptive radiation which has made it possible for these animals to colonize almost all marine, limnic and terrestrial biotopes. In doing so they have evolved a great variety of life forms, and their reproduction and development are correspondingly diverse, with many modes and patterns unique in the animal kingdom. In this special volume recent progress in this broad research area is presented by 26 specialists, in general through surveys or treatments of selected examples. Some of them review important annelid taxa such as the Nereididae, Syllidae, Spionidae, Cirratulidae, Clitellata, and Pogonophora; others analyse reproductive and developmental structures and phenomena in annelids, e.g. segmental organs, sex pheromones, oogenesis, mating systems, sperm types, life cycles, larval settlement, cleavage and symmetry of embryos, or discuss controversial approaches to annelid systematics. The book will be of interest to all zoologists who work with annelids as well as to embryologists and other researchers in reproductive biology.