Book excerpt: Pinnipeds are a fascinating group of marine mammals that play a crucial role as apex predators and sentinels of the functioning and health of marine ecosystems. They are found in the most extreme environments from the Polar regions to the tropics. Pinnipeds are comprised of about 34 species, and of those at least 25% live permanently in tropical zones. This book reviews and updates current research on the biology, marine ecology, bio-monitoring, and conservation of tropical pinniped populations, including their behavior, anthropogenic stressors, and health. It also looks at challenges to be faced for the conservation of tropical pinnipeds, many of which are threatened species.