Whales are the only mammals that spend their entire life in the water. From playful dolphins to enormous blue whales, the behavior, habitats, and physiology of these amazing marine mammals are explored in What is a Whale? Spectacular full-color photos help show:* flukes, flippers, and fins* the whale family tree* baleen and toothed whales* how whales communicate through echolocation* watery homes and what they eat* baby whales* whale-watching and why whales are in danger