Piz Buin (Romansh pronunciation: [ˌpits buˈiːn] ) is a mountain in the Silvretta range of the Alps on the border between Austria and Switzerland . It forms the border between the Swiss canton of Graubünden and the Austrian state of Vorarlberg and is the highest peak in Vorarlberg.

Its full name in the Romansh language is Piz Buin Grond (Great Piz Buin). A similar but smaller summit nearby is called Piz Buin Pitschen (Small Piz Buin) at 3,255 m (10,680 ft). Piz Buin was first climbed on 14 July 1865 by Joseph Anton Specht and Johann Jakob Weilenmann, guided by Jakob Pfitscher and Franz Pöll. Piz Buin Pitschen was climbed three years later.