The United Nations Convention on the Law of the Sea (UNCLOS), also called the Law of the Sea Convention or the Law of the Sea Treaty, is an international agreement that establishes a legal framework for all marine and maritime activities. As of June 2016, 167 countries and the European Union are parties.

The convention resulted from the third United Nations Conference on the Law of the Sea (UNCLOS III), which took place between 1973 and 1982. UNCLOS replaced the four treaties of the 1958 Convention on the High Seas. UNCLOS came into force in 1994, a year after Guyana became the 60th nation to ratify the treaty.

UNCLOS I

In 1956, the United Nations held its first Conference on the Law of the Sea (UNCLOS I) at Geneva, Switzerland. UNCLOS I resulted in four treaties concluded in 1958:

• Convention on the Territorial Sea and Contiguous Zone, entry into force: 10 September 1964
• Convention on the Continental Shelf, entry into force: 10 June 1964
• Convention on the High Seas, entry into force: 30 September 1962
• Convention on Fishing and Conservation of Living Resources of the High Seas, entry into force: 20 March 1966

Although UNCLOS I was considered a success, it left open the important issue of breadth of territorial waters.

UNCLOS II

In 1960, the United Nations held the second Conference on the Law of the Sea ("UNCLOS II"); however, the six-week Geneva conference did not result in any new agreements. Generally speaking, developing nations and third world countries participated only as clients, allies, or dependents of the United States or the Soviet Union, with no significant voice of their own.

UNCLOS III

The issue of varying claims of territorial waters was raised in the UN in 1967 by Arvid Pardo of Malta, and in 1973 the Third United Nations Conference on the Law of the Sea convened in New York. In an attempt to reduce the possibility of groups of nation-states dominating the negotiations, the conference used a consensus process rather than majority vote. With more than 160 nations participating, the conference lasted until 1982. The resulting convention came into force on 16 November 1994, one year after the 60th state, Guyana, ratified the treaty.

The convention introduced a number of provisions. The most significant issues covered were setting limits, navigation, archipelagic status and transit regimes, exclusive economic zones (EEZs), continental shelf jurisdiction, deep seabed mining, the exploitation regime, protection of the marine environment, scientific research, and settlement of disputes.

Internal waters: Covers all water and waterways on the landward side of the baseline. The coastal state is free to set laws, regulate use, and use any resource. Foreign vessels have no right of passage within internal waters. A vessel in the high seas assumes jurisdiction under the internal laws of its flag state.

Territorial sea: Up to 12 nautical miles (22 kilometres; 14 miles) from the baseline, the coastal state is free to set laws, regulate the use, and use any resource, in essence, the coastal State enjoys Sovereign rights and sovereign jurisdiction within its territorial sea. Vessels were given the right of innocent passage through any territorial sea, with strategic straits allowing the passage of military craft as transit passage, in that naval vessels are allowed to maintain postures that would be illegal in the territorial sea. "Innocent passage" is defined by the convention as passing through waters in an expeditious and continuous manner, which is not "prejudicial to the peace, good order or the security" of the coastal state. Fishing, polluting, weapons practice, and spying are not "innocent", and submarines and other underwater vehicles are required to navigate on the surface and to show their flag. Nations can also temporarily suspend innocent passage in specific areas of their territorial sea, if doing so is essential for the protection of their security.

Archipelagic waters: The convention set the definition of "Archipelagic States" in Part IV, which also defines how the state can draw its territorial borders. A baseline is drawn between the outermost points of the outermost islands, subject to these points being sufficiently close to one another. All waters inside this baseline are designated "Archipelagic Waters". The state has sovereignty over these waters mostly to the extent it has over internal waters, but subject to existing rights including traditional fishing rights of immediately adjacent states. Foreign vessels have right of innocent passage through archipelagic waters, but archipelagic states may limit innocent passage to designated sea lanes.

Contiguous zone: Beyond the 12-nautical-mile (22 km) limit, there is a further 12 nautical miles (22 km) from the territorial sea baseline limit, the contiguous zone. Here a state can continue to enforce laws in four specific areas (customs, taxation, immigration, and pollution) if the infringement started or is about to occur within the state's territory or territorial waters.This makes the contiguous zone a hot pursuit area.

Exclusive economic zones (EEZs): These extend 200 nmi (370 km; 230 mi) from the baseline. Within this area, the coastal nation has sole exploitation rights over all natural resources. In casual use, the term may include the territorial sea and even the continental shelf. The EEZs were introduced to halt the increasingly heated clashes over fishing rights, although oil was also becoming important. The success of an offshore oil platform in the Gulf of Mexico in 1947 was soon repeated elsewhere in the world, and by 1970 it was technically feasible to operate in waters 4,000 metres (13,000 ft) deep. Foreign nations have the freedom of navigation and overflight, subject to the regulation of the coastal states. Foreign states may also lay submarine pipes and cables.

Continental shelf: The continental shelf is defined as the natural prolongation of the land territory to the continental margin's outer edge, or 200 nautical miles (370 km) from the coastal state's baseline, whichever is greater. A state's continental shelf may exceed 200 nautical miles (370 km) until the natural prolongation ends. However, it may never exceed 350 nmi (650 km; 400 mi) from the baseline; nor may it exceed 100 nmi (190 km; 120 mi) beyond the 2,500 metres (8,200 ft) isobath (the line connecting the depth of 2 500 m). Coastal states have the right to harvest mineral and non-living material in the subsoil of its continental shelf, to the exclusion of others. Coastal states also have exclusive control over living resources "attached" to the continental shelf, but not to creatures living in the water column beyond the exclusive economic zone.

The area outside these areas is referred to as the "high seas" or simply "the Area".

Aside from its provisions defining ocean boundaries, the convention establishes general obligations for safeguarding the marine environment and protecting freedom of scientific research on the high seas, and also creates an innovative legal regime for controlling mineral resource exploitation in deep seabed areas beyond national jurisdiction, through an International Seabed Authority and the common heritage of mankind principle.

Landlocked states are given a right of access to and from the sea, without taxation of traffic through transit states.