The Aosta Valley (Italian: Valle d'Aosta [ˈvalle daˈɔsta]; French: Vallée d'Aoste [vale dɔst] ; Arpitan: Val d'Aoûta [val duta] ; Walser: Augschtalann or Ougstalland; Piedmontese: Val d'Osta), officially the Autonomous Region of Aosta Valley, is a mountainous autonomous region in northwestern Italy. It is bordered by Auvergne-Rhône-Alpes, France, to the west; by Valais, Switzerland, to the north; and by Piedmont, Italy, to the south and east. The regional capital is Aosta.

Covering an area of 3,263 km2 (1,260 sq mi) and with 122,714 inhabitants as of 2025, it is the smallest, least populous, and least densely populated region of Italy. The province of Aosta having been dissolved in 1945, the Aosta Valley region was the first region of Italy to abolish provincial subdivisions, followed by Friuli-Venezia Giulia in 2017 (where they were reestablished later). Provincial administrative functions are provided by the regional government.