Borders of the United States

Maritime borders that are not delineated by bilateral treaty are defined by United States acceptance of the United Nations Convention on the Law of the Sea (UNCLOS), which includes the convention's exclusive economic zone boundary definitions but does not extend to mineral rights in international waters.

Insular areas in the Pacific and the U.S. Virgin Islands are not included in the main domestic customs territory which is limited to the 50 states, the District of Columbia, and Puerto Rico.

The United States Coast Guard actively patrols the nation's extensive maritime borders, acting as a law enforcement agency in peacetime.

The United States Armed Forces are generally prohibited from domestic law enforcement (including arresting smugglers and illegal immigrants) under the Posse Comitatus Act, but can be activated to secure the border in an emergency or respond to an attack.

State and federal National Guard troops and even active-duty military personnel have been used in support roles at the border, which has been controversial and limited by legal complexities.