Mangareva is the central and largest island of the Gambier Islands in French Polynesia. It is surrounded by smaller islands: Taravai in the southwest, Aukena and Akamaru in the southeast, and islands in the north. Mangareva has a permanent population of 1,641 (2007) and the largest village on the island, Rikitea, is the chief town of the Gambier Islands.

The island is approximately 8 km (5.0 mi) long and, at 18 km² (7 mi²), it comprises about 56% of the land area of the whole Gambier group. Mangareva has a high central ridge which runs the length of the island. The highest point in the Gambiers is Mt. Duff, on Mangareva, rising to 441 m along the island's south coast. The island has a large lagoon 15 miles in diameter containing reefs whose fish and shellfish helped ancient islanders survive much more successfully than on nearby islands with no reefs.