Langau is a town in the district of Horn, in the Austrian state of Lower Austria. It lies in the Waldviertel, the northwestern quarter of Lower Austria, a rural region bordering the Czech Republic.
The town is one of the municipalities that make up the Horn district, an administrative area in the northern part of the state. As with other settlements in the Waldviertel, Langau is set in a landscape of rolling hills, farmland and woodland rather than the alpine terrain associated with western Austria.