Mangareva is the central, and most important island of the Gambier Islands, in French Polynesia. The island is approximately 8 km (5 mi.) long, and at 18 km² (7 mi².), it comprises about 56% of the land area of the whole Gambier group. It has a high central ridge which runs the length of the island.

The largest village on the island, Rikitea, is the chief town of the Gambier Islands.

The highest point in the Gambiers is Mt. Duff, on Mangareva, rising to 482 m (1600 ft) along the island's south coast.

Mangareva was once heavily forested and supported a large population that traded with other islands via ocean-going canoes. However, excessive logging by the islanders during the tenth to the fifteenth centuries resulted in deforestation of the island, with disastrous results for its environment and economy (see Gambier Islands for more details).