Appenzell Ausserrhoden, in English sometimes Appenzell Outer Rhodes, is one of the 26 cantons forming the Swiss Confederation. It is composed of twenty municipalities. The seat of the government and parliament is Herisau, and the seat of judicial authorities are in Trogen. It is traditionally considered a "half-canton", the other half being Appenzell Innerrhoden.

Appenzell was a canton in the northeast of Switzerland, and entirely surrounded by the canton of St. Gallen, in existence from 1403 to 1597.