In maritime law, the waters lying outside the territorial waters of any and all states.
In the Middle Ages, a number of maritime states asserted sovereignty over large portions of the high seas. The doctrine that the high seas in time of peace are open to all nations was first proposed by Hugo Grotius (1609), but it did not become an accepted principle of international law until the 19th century. Activities permitted on the high seas include navigation, fishing, the laying of submarine cables and pipelines, and overflight of aircraft.