Piz Buin 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 original name in the Romansh language is Piz Buin Grand. A similar but smaller summit nearby is called Piz Buin Pitschen at 3,255m (10,680 ft).
Piz Buin can be reached from the Wiesbadener hut in Austria, crossing the Vermunt glacier, climbing up the Wiesbadener ridge and hiking over the Ochsentaler Glacier to the Buin gap. From the gap there is a zigzag walk to the top, with only a 20 m (65 ft) steep step to surmount before reaching the relatively flat summit space, which has an old wooden cross on the very top. The border between Switzerland and Austria crosses the summit from East to West.