Herisau is a municipality of the canton of Appenzell Ausserrhoden in Switzerland. It is the seat of the canton's government and parliament; the judicial authorities are situated in Trogen.

The central hamlet and the houses around the central square, the Protestant church of 1580, the houses Wetter and zur Rose (both 1737), the hamlet Schwänberg and the government building with the state archive are listed as heritage sites of national significance.