Graubünden or Grisons (German: Graubünden, [ɡraʊˈbʏndən] ( listen); French: Grisons, [gʁi'zɔ̃]; Italian: Grigioni[ɡriˈdʒoːni]; Romansh: Grischun [ɡʁiˈʒun] ( listen); see also other names) is the largest and easternmost canton of Switzerland. The canton shares borders with the cantons of Ticino, Uri, Glarus and St. Gallen and international borders with Italy, Austria and Liechtenstein. The name Graubünden translates as the "Grey Leagues," referring to the canton's origin in three local alliances, the League of God's House, the Grey League, and the League of Ten Jurisdictions. Graubünden is also home to three of Switzerland's ethnic groups and the subsequent languages of Swiss German, Italian and Romansh are all native to the state. It is also the only canton where the dialects of the ancient Romansh language are still spoken.

Graubunden is by far Switzerland's largest canton at 7,105.2 square kilometres (2,743.3 sq mi). Only about a third of this is commonly regarded as productive land of which forests cover about a fifth of the total area. The canton is entirely mountainous, comprising the highlands of the Rhine and Inn river valleys. In its southeastern part lies the only official Swiss National Park. In its northern part the mountains were formed as part of the thrust fault that was declared a geologic UNESCO World Heritage Site, under the name Swiss Tectonic Arena Sardona, in 2008. Another Biosphere Reserve is the Biosfera Val Müstair adjacent to the Swiss National Park whereas Ela Nature Park is one of the regionally supported parks.