There are minerals, natural gas, and oil deposits on the islands and their nearby seafloor. Because of the economic, military, and transportational importance, the control, especially of the Spratlys, has been in dispute by China and several Southeast Asian countries such as Vietnam from the mid-20th century onwards. True occupation and control are shared between the claimants. (See Claims and control)
The South China Sea Islands were collectively named the Tough Heads of the Surging Sea (漲海崎頭 Zhànghǎi Qítóu) and Coral Cays (珊瑚洲 Shanhu Zhou) since their discovery by the Chinese in the Qin Dynasty. But seafaring did not occur until the next dynasty, the Han Dynasty. After the Song Dynasty, the Islands had been called The Thousand-Mile Long Sands (千里長沙) and Myriad-Mile Stony Embankment (萬里石塘).
There are houses dated back to the Tang or Song Dynasty on Ganquan Island (甘泉島), which nowadays is under dispute with Vietnam. In 1045, during the reign of Emperor Renzong of Song China, imperial troops (王師) were sent to the Paracel Islands. The fishermen of Hainan composed various "Notebooks on Paths and Timing" (更路簿) that recorded over 200 routes, the time needed for sailing among the different isles, and the names of over 100 islands commonly used by the fishermen.
Some of the voyages of Zheng He passed by the Islands, though they probably did not dock on them. There is an atoll in the Spratly Islands named after Zheng He though.
Vietnamese fishermen and merchants also have been exploring the South Sea Islands, with a well-known presence, due to the historically unofficial capacity and shorter records. Vietnamese official documents cite Vietnamese ancient historical records of control and exploitation of the island, and dispute Chinese claims and records.
In the 19th century, as a part of the occupation of Indochina, France claimed control of the Spratlys until the 1930s, exchanging a few with the British. During World War II, the Islands were annexed by Japan.
The People's Republic of China (PRC) claims all of these islands as part of its Hainan Province, at the administrative level of banshichu (辦事處/办事处). The PRC strongly asserted its claims to the islands, but in the late 1990s, under the new security concept, the PRC put its claims less strongly.
On the other hand, Vietnam claims all Spratly Islands belong to a district, first in 1973, of the Phuoc Tuy Province, then, of the Khanh Hoa Province.
Currently, Vietnam occupies twenty-nine islands or rocks, while the People's Republic of China occupies eight or nine.
In addition to the People's Republic of China and Vietnam, the Republic of China (Taiwan), Malaysia and the Philippines also claim and occupy some islands. Taiwan claims all the Spratly Islands, but only occupies one island and one shelf including Itu Aba (Taiping). Malaysia occupies three islands on its continental shelf. The Philippines claims most of the Spratlys and calls it the Kalayaan Group of Islands, and they form a distinct municipality in the province of Palawan. The Philippines, however, only occupies eight islands.
The islands are located on a shallow humite-layer continental shelf with an average of 200 metres deep. However, in the Spratlys, the sea floor drastically changes its depth, and near the Philippines, the Palawan Trough is more than 5,000 metres deep. Also, there are some parts that are so shallow that navigation becomes difficult, and prone to accidents.
There are around 100–200 plant species on the Islands altogether. For example, the Paracels have 166 species, but later the Chinese and the Vietnamese introduced 47 more species, including peanut, sweet potato, and various vegetables.