The alto trombone is generally pitched in E-flat, a perfect fourth above the more common tenor trombone, although Olds and others have produced alto trombones a step higher, in F. Modern alto trombones use a tenor trombone mouthpiece.
Like other members of the slide trombone family, the alto trombone has a seven-position slide for changing the pitch. Some modern alto trombones have a trigger for a rotary valve. On some models that rotary valve lowers the pitch a perfect fourth, as it does on the F-attachment tenor or single-rotor bass trombone; by lowering the pitch by a fourth, the alto trombone thus can achieve the range of a valveless tenor trombone. On other models, the rotary valve serves as a trill valve.
Although less common, the alto trombone is also made in a valve trombone configuration. For a fine example, see the DVD, "German Brass Goes Bach".
Alto trombone music is notated in the alto clef—the same clef in which viola music is traditionally notated. For example, the following three excerpts from "Brown Wore Black" are equivalent:
As the example shows, the advantage of using alto clef for alto trombone music is that it lets notes that fall within the alto trombone's midrange be notated within the staff, thus trading the difficulty of learning a different clef for the difficulty of reading music with a large number of ledger lines.
Historically, the alto trombone has found a place in the symphony orchestra, playing the highest parts in the symphonies of Beethoven and his contemporaries. The alto trombone has also had a regular role in the Moravian trombone choir and its modern descendents. Furthermore, in the 20th century the alto trombone enjoyed a growing solo literature.