Marshall Belford Allen (born May 25, 1924) is an American free jazz and avant-garde jazz alto saxophone player. He also performs on flute, oboe, piccolo, and EVI (an electronic valve instrument made by Steiner, Crumar company).
Allen is best known for his work with Sun Ra, having recorded and performed mostly in this context since the late 1950s, and having led Sun Ra's Arkestra since 1993. Critic Jason Ankeny describes Marshall as "one of the most distinctive and original saxophonists of the postwar era."