Ua Pu (also known as Ua Pou) is the third largest of the Marquesas Islands, located about 50 km (30 mi.) south of Nuku Hiva, in the northern Marquesas. Until recently, it was the most populous of the islands, owing to the fact that when the other islands were being ravaged by diseases introduced by European explorers and traders, the Catholic priests on Ua Pu finally took to quarantining the remnant of the native population inside their churches whenever visiting ships approached the island, thereby reducing their exposure to external diseases.

The centre of the island is characterized by four high basalt pillars that reach high above the surrounding mountains. The highest of these pillars reaches to 1,232 m (4,042 ft.) above sea level and is the highest elevation in the Marquesas.

The island covers an area of 105 km (41 sq. mi.), and is located just northwest of the small island of Motu ‘Oa. The population in 2002 was 2,013. The largest village is on Haka Hau bay, on the northeast coast.