Marine mammals command a high level of public attention, reflected in specific legislation for their protection and management in many countries. They also present particular challenges to ecologists and conservation biologists. They are mostly difficult to observe, they occupy an environment that is vast in its three dimensional extent, there are often perceived conflicts between marine mammals and people, and furthermore several species are now close toextinction. Marine mammals have some intriguing features in their biology - the ability to dive to crushing depths, to perform breath-hold dives that defy our current understanding of mammalian physiology, and many have an ability to hunt down prey using sophisticated sonar that we are only just beginning to understand. Many species also have complex social structures. We still have much to learn about these extraordinary animals so a comprehensive and authoritative overview of current methodology is nowtimely. The intention of this book is both to summarize the state-of-the-art and to encourage innovation and further progress in this research field.