The scientific community and the public have become increasingly aware of, and concerned about, underwater sound. There is a need to increase understanding the degree to which anthropogenic activities may be changing the underwater soundscape, how these changes may potentially impact marine animals , and what action can be taken to mitigate these potential impacts. In accordance with the Marine Mammal Protection Act (MMPA), marine mammals cannot be hunted, harassed, captured, or killed. Individuals must apply for a permit in order to conduct research and/or other activities that may impact marine mammals. Incidental Harassment Authorizations (IHAs) or Letters of Authorization (LOA) may be issued to groups incidentally “taking” small numbers of marine mammals and/or casing a “neglible impact”. Most IHAs and LOAs have involved the incidental harassment of marine mammals by noise (airguns , ships and aircraft, high energy sonars, and explosive detonations ). The National Oceanic and Atmospheric Administration (NOAA) is developing science-based acoustic guidelines for assessing the effects of anthropogenic sound on marine mammals. This will help guide the permit process. Draft guidelines are also being considered by the International Maritime Organization (IMO) to reduce underwater noise from commercial ships, giving special consideration to propulsion, hull design, onboard machinery, and operational modifications.