This open-access book invites its readers to dive into the depths of marine mammal bioacoustics. The ocean is a noisy place—naturally as well as anthropogenically. Our book explores the fundamentals of ocean acoustics, revealing the intricate sources of underwater noise that challenge marine life. Readers delve into the unique vocalizations of mysticetes, odontocetes, pinnipeds, otters, and sirenians, uncovering their diverse communication in stormy waters. The book presents research on marine mammal hearing and the impact of noise on their physiology and behavior, from the subtle behavioral responses to the broader biological significance of these effects. With insights into the management of anthropogenic noise, this book equips students, researchers, environmental managers, policy makers, conservationists, and enthusiasts alike with vital knowledge for protecting our ocean’s acoustic environments.