Ua Pu (, North Marquesan: ’uapou) is the third largest of the Marquesas Islands, in French Polynesia, an overseas territory of France in the Pacific Ocean. It is located about 50 km (30 mi.) south of Nuku Hiva, in the northern Marquesas. Until the beginning of the 1980s, it was the most populous of the Marquesas Islands, because when the other islands were being ravaged by diseases introduced by European explorers and traders, the Catholic priests on the island 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.