Hainan is an island province and the southernmost province of China consisting of the eponymous Hainan Island and various smaller islands in the South China Sea under the province's administration. The name literally means "South of the Sea".

The province has a land area of 33,920 square kilometers (13,100 sq mi), of which Hainan Island is 32,900 square kilometers (12,700 sq mi) and the rest is over 200 islands scattered across three archipelagos: Zhongsha, Xisha and Nansha. It was part of Guangdong from 1950 to 1988, after which it was made a province of its own and was designated as a special economic zone by Deng Xiaoping, as part of the Chinese economic reform program.

The Han Chinese population, who compose a majority of the population at 82%, speak a wide variety of languages including Standard Chinese, Hainam Min, Yue Chinese, Cantonese, Hakka Chinese, etc. Indigenous peoples such as the Hlai, a Kra–Dai-speaking ethnic group, are native to the island and compose 15% of the population. Their native languages include the Hlai languages. The Hlai are recognized by the Chinese government as one of the country's 56 ethnic groups. Speakers of Be, despite speaking a Kra-Dai language, are reckoned officially as ethnically Han Chinese. Hainan is also home to the Jiamao language, of disputed provenance.

There are ten major cities and ten counties in Hainan Province. The capital of the province is Haikou, on the northern coast of Hainan Island, while Sanya is a well-known tourist destination on the southern coast. The other major cities are Wenchang, Sansha, Qionghai, Wanning, Wuzhishan, Dongfang and Danzhou.

According to China's territorial claims, several disputed territories in the South China Sea, including the Spratly Islands (Nansha) and Paracel Islands (Xisha), are administered under Sansha city of the province. While the Paracels are fully under China's control, many of the Spratly Islands are controlled by other countries, such as Vietnam and the Philippines.

In 2020, a large-scale plan was announced by the Chinese government to transform the entire island province into a free trade port, with the aim of turning it into the largest free-trade port in the world by 2035. The plan involves building a hub for offshore financing and duty-free shopping, as well as using lower taxes and reduced visa requirements to help draw in foreign businesses and tourists. Moreover, all goods sold from Hainan to other parts of China would be treated as imports from 2025 onward. Chinese officials announced that the Hainan Free Trade Port will launch island-wide independent customs operations on December 18, 2025.

The provincial name derives from its major island, Hainan, in Hainanese "Hai Nam", which is named after its position south of the Qiongzhou Strait. (To the north of the strait, the Leizhou Peninsula in Guangdong is also known as Haibei/Hai Bac or "North of the Sea".) Former names for Hainan Island include Zhuya, Qiongya, and Qiongzhou. The latter two gave rise to the provincial abbreviation 琼 (Qióng/Kheng).

During the 17th and 18th centuries, explorers referred to the island as "Aynam", which remains the pronunciation of its name in the local Hainanese dialect.