This comprehensive book provides new insights into the morphological, metabolic, thermoregulatory, locomotory, diving, sensory, feeding, and sleep adaptations of Cetacea (whales and dolphins), Pinnipedia (seals, sea lions and walrus), Sirenia (manatees and dugongs) and sea otters for an aquatic life. Each chapter reviews the discoveries from previous studies and integrates recent research using new techniques and technology. Readers will gain an understanding of the remarkable adaptations that enable marine mammals to spend all or most of their lives at sea, often while hunting prey at depth.