Dax is a commune in Nouvelle-Aquitaine, southwestern France, sub-prefecture of the Landes department.

Nouvelle-Aquitaine is the largest administrative region in France by area, spanning the west and southwest of Metropolitan France. The region was created in 2014 by the merging of Aquitaine, Limousin, and Poitou-Charentes in a territorial reform. Nouvelle-Aquitaine has an area of 84,035.7 km2 (32,446.4 sq mi) – more than 1⁄7 of Metropolitan France – and has a population of 6,033,952 as of 2020. The new region was established on 1 January 2016, following the regional elections in December 2015.