Rennell Island, locally known as Mugaba, is the main island of two inhabited islands that make up the Rennell and Bellona Province in the nation state of Solomon Islands. Rennell Island has a land area of 660 square kilometres (250 sq mi) that is about 80 kilometres (50 mi) long and 14 kilometres (8.7 mi) wide. It is the second largest raised coral atoll in the world with the largest lake in the insular Pacific, Lake Tegano, a lake that is listed as a World Heritage Site. Rennell Island has a population of about 1,840 persons of Polynesian descent who primarily speak Rennellese, Pijin and some English. Rennell and Bellona Islands are two of the few islands in the otherwise Melanesian Solomon Islands archipelago classified as a Polynesian outlier; others being Sikaiana, Ontong Java, Tikopia, Anuta, Duff Islands, and some Reef Islands.

Rennell and Bellona is one of the nine provinces of Solomon Islands, comprising two inhabited atolls, Rennell and Bellona, or Mu Ngava and Mu Ngiki respectively in Rennellese, as well as the uninhabited Indispensable Reef. Rennell and Bellona are both Polynesian-inhabited islands within the predominantly Melanesian Solomons. They are thus considered Polynesian outliers. The first known European to sight the islands was Mathew Boyd of Camberwell, London, commander of the merchant ship, Bellona, in 1793. The province has a combined population of 3,041, the least populous province of Solomon Islands. The Samoic language of the islands is, in English texts, called Rennellese. The province's capital is Tigoa, on Rennell Island.