An instrument in the Western concert flute family, the second-highest member below the standard C flute. It is the third most common member of its family after the standard C flute and the piccolo. It is characterised by its rich, mellow tone in the lower portion of its range. It is a transposing instrument in G (a perfect fourth below written C), and uses the same fingerings as the C flute. 

The bore of the alto flute is considerably larger in diameter and longer than a C flute and requires more breath from the player. This gives it a greater dynamic presence in the bottom octave and a half of its range.

British music that uses this instrument often refers to it as a bass flute, which can be confusing since there is a distinct instrument known by that name. This naming confusion originated in the fact that the modern flute in C is pitched in the same range as the Renaissance tenor flute, and so a lower pitched instrument would logically be called a bass.