The Vienna Boys' Choir (also the Vienna Choir Boys, German: Wiener Sängerknaben) is a choir of trebles and altos based in Vienna. It is one of the best known boys' choirs in the world. The boys are selected mainly from Austria, but also from many other countries around the world, and individually interviewed. Over the centuries, the choir has worked with many composers including Mozart, Caldara, Salieri, Heinrich Isaac, Hofhaimer, Biber, Fux, Gluck, and Bruckner.