The rules governing who can do what on the sea are mostly set out in the United Nations Convention on the Law of the Sea, or UNCLOS, which was adopted in 1982 and came into force in 1994. UNCLOS establishes the territorial sea, an area extending 12 nautical miles from a coastal state's baseline in which it has full sovereignty, and the Exclusive Economic Zone, or EEZ, extending 200 nautical miles offshore, where the coastal state has rights to explore, exploit, and manage natural resources. Beyond the EEZ lie the international waters, sometimes called the high seas, which are open to all states for navigation, fishing, and scientific research. The continental shelf — the seabed extending from the coast to where the geological margin drops off — generally extends up to 200 nautical miles, though it may be claimed further where the natural geology justifies it.
A relatively small number of ports handle a disproportionate share of the world's shipping. The Port of Shanghai, located at the mouth of the Yangtze River in China, is the busiest port on Earth by cargo tonnage. The Port of Singapore, sitting on the Strait of Malacca, handles over 37 million TEUs (twenty-foot equivalent units) per year and is one of the world's leading transshipment hubs. The Port of Rotterdam in the Netherlands is the largest port in Europe and a major gateway for trade with the continent's interior, while the Port of Dubai at Jebel Ali is the largest in the Middle East and a key transshipment point between Asia, Europe, and Africa. Mumbai, formerly Bombay, has long served as India's historic gateway to the sea and remains the country's busiest port.
Together, these ports, canals, straits, and international legal frameworks form a global maritime system that links continents and economies. The strategic value of key chokepoints — from the Suez and Panama Canals to the Straits of Hormuz, Malacca, and Gibraltar — means that even small disruptions can ripple through worldwide supply chains. Understanding this system, from the deepest ocean zones and largest rivers to the busiest ports and narrowest straits, is essential to grasping how oceans and waterways shape the modern world.