The United Nations Convention on the Law of the Sea is an international agreement that defines the rights and responsibilities of nations in their use of the world's oceans and management of their natural resources.

Nations participating in the third U.N. Conference on the Law of the Sea reached agreement on the treaty in 1982 after nine years of deliberations. The convention took effect in 1994 after the requisite minimum of 40 states had ratified it. As of May 2011, 161 states and the European Union had ratified the treaty.

The convention set the limits of various sea areas, measured from the baseline of coastal states. The areas include internal waters, territorial waters, contiguous zones, archipelagic waters, exclusive economic zones and continental shelves.

Internal waters cover all water and waterways on the landward side of a coastal state's baseline. The state has full sovereignty over such waters.

The convention says a coastal state has the right to establish territorial waters up to 22 kilometers from the baseline. The state is free to exercise its sovereignty over those waters but must grant the right of “innocent passage” through those areas to ships of all other states.

Innocent passage is defined as the “continuous and expeditious” movement of a foreign vessel that does not prejudice the “peace, good order or security” of the coastal state. Actions that are deemed to be prejudicial include spying, military exercises, polluting and fishing.

The treaty enables a coastal state to set up a contiguous zone beyond its territorial waters to prevent foreign ships from violating the state's laws on customs, taxation, pollution and immigration. The contiguous zone may not extend beyond 44 kilometers from the baseline.

A state that consists of an archipelago can set its territorial boundaries by drawing baselines joining the outermost points of the outermost islands, provided such points are sufficiently close to one another.

The convention defines the area enclosed within those baselines as archipelagic waters and grants the state full sovereignty over them. It also establishes a right of innocent passage through those waters to ships of all other states.

An exclusive economic zone is defined as an area beyond a coastal state's territorial waters that may extend up to 370 kilometers from that state's baseline.

Inside the zone, the treaty says the coastal state has the right to exploit all of its natural resources while respecting the rights of other states. Foreign nations have the rights of navigation, overflight and laying submarine cables and pipelines subject to the regulation of the coastal state.

A continental shelf is defined as a “natural prolongation” of a coastal state's land territory to the outer edge of the continental margin, or a distance 370 kilometers from the state's baseline, whichever is greater. The continental shelf may not exceed 648 kilometers from the baseline.

The treaty says a coastal state has the right to harvest mineral and non-living material in the seabed of its continental shelf. It says no foreign vessel may undertake such activities without the express consent of the coastal state.

In recent months, the Philippines and Vietnam have reported several incidents involving Chinese vessels within their exclusive economic zones in the South China Sea.

China says the South China Sea is Beijing's territory and has been for centuries. But, the Philippines, Vietnam, Brunei, Taiwan and Malaysia also claim parts of the sea and scores of uninhabited islets and outcroppings in the region.

China ratified the U.N. convention in 1996.