Marshall Belford Allen is an American free jazz and avant-garde jazz alto saxophone player. He also performs on flute, oboe, piccolo, and the electronic EWI.

The alto saxophone is a member of the saxophone family of woodwind instruments. Saxophones were invented by Belgian instrument designer Adolphe Sax in the 1840s and patented in 1846. The alto saxophone is pitched in the key of E♭, smaller than the B♭ tenor but larger than the B♭ soprano. It is the most common saxophone and is used in popular music, concert bands, chamber music, solo repertoire, military bands, marching bands, pep bands, carnatic music, and jazz.