Territorial waters, in international law, that area of the sea immediately adjacent to the shores of a state and subject to the territorial jurisdiction of that state. Territorial waters are thus to be distinguished on the one hand from the high seas, which are common to all countries, and on the other from internal or inland waters, such as lakes wholly surrounded by the national territory or certain bays or estuaries.
Historically, the concept of territorial waters originated in the controversy over the status of the sea in the formative period of modern international law in the 17th century. Although the doctrine that the sea by its nature must be free to all was eventually upheld, most commentators did recognize that, as a practical matter, a coastal state needed to exercise some jurisdiction in the waters adjacent to its shores. Two different concepts developed—that the area of jurisdiction should be limited to cannon-shot range, and that the area should be a much greater belt of uniform width adjacent to the coast—and in the late 18th century these concepts coalesced in a compromise view that proposed a fixed limit of 3 nautical miles (1 marine league, or 3.45 statute miles [5.5 km]). In 1793 the United States adopted three miles for neutrality purposes, but although many other maritime states during the 19th century came to recognize the same limit, it never won such universal acceptance as to become an undisputed rule of international law.
In the course of this historical development, it became settled that the belt of territorial waters, together with the seabed and subsoil beneath it and the airspace above, is under the sovereignty of the coastal state. This sovereignty is qualified only by a right of innocent passage—that is, peaceful transit not prejudicial to the good order or security of the coastal state—for merchant vessels of other nations. The right of innocent passage does not apply to submerged submarines or to aircraft, nor does it include a right to fish.
On the width of the belt there has developed no universal agreement except that every state is entitled to a minimum of three nautical miles. Claims in excess of 12 nautical miles (22 km) commonly meet widespread opposition from other states, though in the 1960s and ’70s a trend to a 12-nautical-mile limit was evident; among about 40 states taking this view were China, India, Mexico, Pakistan, Egypt, and the Soviet Union.
Distinct from territorial waters proper are zones in the adjacent high seas in which coastal states claim no territorial rights but assert limited jurisdiction for one or more special purposes. These contiguous zones of 6 to 12 nautical miles (11 to 22 km) beyond territorial waters are most commonly claimed for the enforcement of customs and sanitary regulations, but in some instances they may be established for fishery protection or for security. Also distinct from territorial waters are the claims made after 1945 by many states to the continental shelf off their shores, in or on which potentially valuable resources might exist. Such claims met with little objection from other states when confined to the shelf itself, without affecting the status as high seas of the waters above, but actions by some states, such as Chile, Ecuador, and Peru, that asserted jurisdiction over waters as well as shelf for as much as 200 nautical miles (370 km) offshore evoked wide protest as amounting to unacceptable extensions of territorial waters.
A United Nations Conference on the Law of the Sea that was convened at Geneva in 1958 and attended by 86 nations developed a convention affirming the commonly accepted principles of the legal nature of the territorial sea and the right of innocent passage. This convention took effect in 1964 and by 1970 had been ratified by almost 40 states. A more comprehensive Law of the Sea treaty was signed by 117 nations in 1982. See also high seas.