The oceans cover more than two-thirds of the planet, yet they are not a lawless free-for-all. A single treaty, the United Nations Convention on the Law of the Sea, sets out who controls which waters, where ships can sail, and who may drill, fish, and mine. Often called the constitution for the oceans, it turns the seemingly borderless sea into a series of clearly defined zones.
The treaty behind the rules
Agreed in 1982 and in force since 1994, the Convention was the product of years of negotiation among more than a hundred countries. It replaced a patchwork of older customs and rival claims with a common framework. Most of the world's nations have joined it, and even states that have not formally ratified it, such as the United States, largely treat its core rules as binding custom.
Zones measured from the coast
The genius of the Convention is that it measures maritime rights outward from a country's coastline, using a baseline usually set at the low-water mark. From there, the sea is divided into bands, each with different rules:
- Territorial sea, up to 12 nautical miles from shore, where the coastal state is nearly sovereign, though foreign ships keep a right of innocent passage.
- Contiguous zone, up to 24 miles, where a country can enforce customs, immigration, and health laws.
- Exclusive economic zone, up to 200 miles, where the state controls fishing, oil, gas, and other resources but cannot block free navigation.
- Continental shelf, the seabed extending from the land, where a country holds rights to resources on and under the ocean floor, sometimes beyond 200 miles.
- The high seas, beyond national zones, open to all countries for navigation, overflight, fishing, and research.
Freedom of navigation
One of the treaty's central principles is that ships must be able to move. Even within another country's territorial sea, vessels enjoy innocent passage, meaning they can pass through peacefully without stopping or threatening the coastal state. Through international straits, warships and commercial vessels alike have even stronger transit rights. These freedoms keep global trade flowing, since almost everything shipped between continents crosses waters that touch some nation's zone.
Resources and the deep seabed
The Convention also decides who profits from the sea. Within its exclusive economic zone, a country owns the rights to fish stocks and mineral wealth, which is why coastal states guard these waters closely. Beyond national limits, the deep seabed and its minerals are declared the common heritage of humankind, managed by an international authority so that no single country can simply seize them. As demand grows for metals used in batteries, this once-obscure rule has become the center of a heated debate over deep-sea mining.
Settling disputes
Because maps and coastlines overlap, disputes are inevitable. The Convention created mechanisms to resolve them peacefully, including a dedicated International Tribunal for the Law of the Sea and arbitration panels. These bodies have ruled on boundary disagreements and resource conflicts. Their limitation is enforcement: a tribunal can declare who is right, but it cannot compel a powerful state to comply, as some high-profile cases have shown.
Why it matters on land
The Law of the Sea might sound distant, but it shapes daily life. It determines where your seafood is caught, keeps shipping lanes open so goods reach store shelves, governs undersea internet cables, and sits at the heart of tense standoffs over contested waters. Understanding its zones makes many international news stories, from fishing disputes to naval patrols, suddenly clear.