The United States has land borders with only Canada and Mexico, both of them long. It has maritime boundaries with many countries due to its extensive exclusive economic zone (EEZ). All of its maritime borders with Canada are at least partially disputed, and its territorial claims on three Caribbean islands are disputed.

List

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. United States Minor Outlying Islands (USMOI) are mostly uninhabited, unorganized, and unincorporated.

Custom territories

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.

Border disputes

Disputed occupation

The United States administers Guantanamo Bay Naval Base on what both countries agree is the sovereign territory of Cuba under a permanent lease obtained under the Cuban–American Treaty of Relations (1903), while Cuba was under American military occupation after the 1898 Spanish–American War. After the Cuban Revolution in the 1950s, Cuba disputed the validity of this lease and ceased cooperating with the base. The boundary is highly militarized, but the United States has maintained control without active fighting.

Enforcement

Three agencies in the federal Department of Homeland Security split border-related responsibilities. U.S. Customs and Border Protection staffs official border checkpoints, collects tariff duties, and inspects arriving people, and inspects goods being imported by land, sea, and air. U.S. Immigration and Customs Enforcement polices borders away from official points of entry. United States Citizenship and Immigration Services administers immigration procedures. 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. The border search exception to the guarantees in the Fourth Amendment to the United States Constitution against unreasonable search and seizure and requirement for search warrants apply to border checkpoints and areas within 100 mi of the border.