Odontocetes produce and listen to sound in support of their major life functions, which include foraging, mating, rearing of young, and navigating. Odontocetes are considered highly social animals and acoustic communication plays an important role in all social encounters and in the coordination of group behaviors. Many species, such as bottlenose dolphins and beluga whales, produce sound prolifically. Out of the ~80 species of odontocetes, only ~10 of the most cryptic have not had their vocalizations described. In addition to emitting sounds for communication, odontocetes also emit biosonar sounds for echolocation. In this chapter, we explain how echolocation works and how well the dolphin biosonar system performs. We discuss biosonar design features and how they differ between species. We then discuss odontocete communication sounds, their acoustic features, and functions. We provide a comparative taxonomic overview of odontocete sounds in tables and figures.