Haikou is the capital and most populous city of the Chinese province of Hainan. Haikou city is situated on the northern coast of Hainan, by the mouth of the Nandu River. The northern part of the city is on the Haidian Island, which is separated from the main part of Haikou by the Haidian River, a branch of the Nandu. Administratively, Haikou is a prefecture-level city, comprising four districts, and covering 2,280 square kilometres (880 sq mi). There are 2,046,189 inhabitants in the built-up area, all living within the four urban districts of the city.

Hainan is an island province of the People's Republic of China (PRC), consisting of the eponymous Hainan Island and various smaller islands in the South China Sea under the province's administration. It is the southernmost province of China, and the name means "south of the sea", reflecting the island's position south of the Qiongzhou Strait, which separates it from Leizhou Peninsula of the Chinese mainland.