The part of the ocean adjacent to the coast of a state that is considered to be part of the territory of that state and subject to its sovereignty.
In international law the term territorial waters refers to that part of the ocean immediately adjacent to the shores of a state and subject to its territorial jurisdiction. The state possesses both the jurisdictional right to regulate, police, and adjudicate the territorial waters and the proprietary right to control and exploit natural resources in those waters and exclude others from them. Territorial waters differ from the high seas, which are common to all nations and are governed by the principle of freedom of the seas. The high seas are not subject to appropriation by persons or states but are available to everyone for navigation, exploitation of resources, and other lawful uses. The legal status of territorial waters also extends to the seabed and subsoil under them and to the airspace above them.
From the eighteenth to the middle of the twentieth century, international law set the width of territorial waters at one league (three nautical miles), although the practice was never wholly uniform. The United States established a three-mile territorial limit in 1793. International law also established the principle that foreign ships are entitled to innocent passage through territorial waters.
By the 1970s, however, more than forty countries had asserted a twelve-mile limit for their territorial waters. In 1988 President ronald reagan issued Executive Proclamation 5928, which officially increased the outer limit of U.S. territorial waters from three to twelve miles (54 Fed. Reg. 777). This limit also applies to Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, and the Northern Mariana Islands. The Reagan administration claimed the extension of the limit was primarily motivated by national security concerns, specifically to hinder the operations of spy vessels from the Soviet Union that plied the U.S. coastline. Another reason for the extension was the recognition that most countries had moved to a twelve-mile limit. In 1982, at the Third United Nations Conference on the Law of the Sea, 130 member countries ratified the Convention on the law of the sea, which included a recognition of the twelve-mile limit as a provision of customary international law. Although the United States voted against the convention, 104 countries had officially claimed a twelve-mile territorial sea by 1988.