Michael IX Palaiologos or Palaeologus (Greek: Μιχαήλ Δούκας Ἄγγελος Κομνηνός Παλαιολόγος, Mikhaēl Doukas Angelos Komnēnos Palaiologos; 17 April 1277 – 12 October 1320), was Byzantine Emperor together with his father Andronikos II Palaiologos from 1294 until his death. Andronikos II and Michael IX ruled as equal co-rulers, both using the title autokrator.

A man of impeccable morals and a good helper to his father, he was also known as a brave and energetic soldier, willing to make personal sacrifices to pay or encourage his troops; the Catalan military chronicler Ramon Muntaner said about him: "Emperor Michael was one of the bravest knights in the world". Despite his military prestige, he suffered several defeats, for unclear reasons: his inability as a commander, the deplorable state of the Byzantine army or just simply bad luck.

His premature death at age 43 was attributed in part to grief over the accidental murder of his younger son Manuel Palaiologos by retainers of his older son and later co-emperor Andronikos III Palaiologos.

In the memory of the Byzantines, Michael IX remained "the most pious lord" and "a true emperor in name and deeds".