This book is addressed to the readers operating in the sea urchin field of research, as well as to the lovers of this fascinating organism. Sea urchin, among the most known marine invertebrates belonging to the deuterostomes, is more closely related to humans than other invertebrates, thus representing a suitable model system not only for developmental biology and ecotoxicology but also for biomedicine. The topics described highlight the validity and versatility of this organism for different kinds of investigations. A collection of interesting chapters contributes to this volume and clearly shows the reason of the high interest manifested by a huge number of scientists around the world for this organism over time. Each contribution is a separate and comprehensive chapter but within the book's aim.