The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Philippines (mainly Luzon, Mindoro and Palawan), and in the south by Borneo, eastern Sumatra and the Bangka Belitung Islands, encompassing an area of around 3,500,000 km² (1,400,000 sq mi). It communicates with the East China Sea via the Taiwan Strait, the Philippine Sea via the Luzon Strait, the Sulu Sea via the straits around Palawan (e.g. the Mindoro and Balabac Straits), the Strait of Malacca via the Singapore Strait, and the Java Sea via the Karimata and Bangka Straits. The Gulf of Thailand and the Gulf of Tonkin are also part of South China Sea. The shallow waters south of the Riau Islands are also known as the Natuna Sea.

South China Sea is a region of tremendous economic and geostrategic importance. One-third of the world's maritime shipping passes through it, carrying over US$3 trillion in trade each year. Huge oil and natural gas reserves are believed to lie beneath its seabed. It also contains lucrative fisheries, which are crucial for the food security of millions in Southeast Asia.

The South China Sea Islands, collectively comprising several archipelago clusters of mostly small uninhabited islands, islets (cays and shoals), reefs/atolls and seamounts numbering in the hundreds, are subject to competing claims of sovereignty by several countries. These claims are also reflected in the variety of names used for the islands and the sea.