For the 119 species of marine mammals, as well as for some other aquatic animals, sound is the primary means of learning about their environment and of communicating, navigating, and foraging. Ambient noise and its potential impacts have been regulated since the passage of the Marine Mammal Protection Act of 1972; however, public awareness of the issue has escalated in the past decade when researchers began using high-intensity sound to measure ocean climate changes and stranding of beaked whales occurred in proximity to U.S. Navy sonar use. This report reviews sources of noise in the ocean environment, what is known of the responses of marine mammals to acoustic disturbance, and what models exist for describing ocean noise and marine mammal responses. Recommendations are made for future data gathering efforts, studies of marine mammal behavior and physiology, and modeling efforts necessary to determine what the long- and short-term impacts of ocean noise on marine mammals.