Valais (UK: VAL-ay, US: val-AY, French: [valɛ] (listen); Arpitan: Valês; German: Wallis [ˈvalɪs] (listen)), more formally the Canton of Valais, is one of the 26 cantons forming the Swiss Confederation. It is composed of thirteen districts and its capital and largest city is Sion. The flag of the canton is made of thirteen stars representing the districts, on a white-red background.

Valais is situated in the southwestern part of the country. It borders the cantons of Vaud and Bern to the north, the cantons of Uri and Ticino to the east, as well as Italy to the south and France to the west. It is one of the three large southern Alpine cantons, along with Ticino and the Grisons, which encompass a vast diversity of ecosystems. It is a bilingual canton, French and German being its two official languages. Traditionally, the canton is divided into Lower, Central, and Upper Valais, the latter region constituting the German-speaking minority.

Valais essentially coincides with the valley of the Rhône from its headwaters to Lake Geneva, separating the Pennine Alps from the Bernese Alps, the two largest mountain ranges of the canton. A major wine region, the canton is simultaneously one of the driest regions of Switzerland in its central Rhône valley and among the wettest, having large amounts of snow and rain upon the highest peaks found in Switzerland, such as Monte Rosa and the Finsteraarhorn. Although a major hydroelectricity producer, Valais is essentially renowned for its tourism industry and its numerous Alpine resort towns, notably Crans-Montana, Saas Fee, Verbier, and Zermatt. Overlooking the latter town, the Matterhorn has become an iconic landmark of the canton.

In 1529, Valais became an associate member of the Swiss Confederation. After having resisted the Protestant Reformation and remained faithful to the Roman Catholic Church, it became a republic under the guidance of the prince-bishop of Sion in 1628. In 1815, Valais finally entered the Swiss Confederation as a canton. In 1878, the Simplon Railway connected most of Valais with the cities of the Swiss Plateau. The canton was further opened up by the Lötschberg Railway in 1913.