Abu Abdullah Musa ibn Mahdi al-Hadi (d. September 14, 786) was an Abbasid caliph who succeeded his father Al-Mahdi and who ruled from 785 until his death in 786.

Al-Hadi was the eldest son of Al-Mahdi, like his father he was very open to the people of his empire and allowed commoners to visit him in the palace at Baghdad to address him. As such, he was considered an enlightened ruler, and continued the progressive moves of his Abbasid predecessors.

His short rule was wreaked with numerous military conflicts though. The revolt of Husayn bin Ali bin Hasan broke out when Husayn declared himself caliph in Medina. Al-Hadi crushed the rebellion and killed Husayn and most of his followers, but one cousin of Husayn escaped to Morocco where he would set up the Idrisi state . al-Hadi would also have to crush a Kharijite rebellion as well as face a Byzantine invasion. However, the Byzantines were turned back, and the Abbasid armies actually seized some territory from the Byzantines.

Al-Hadi died in 786 of natural causes. Some have claimed that he was assassinated by someone who was hired by his own mother, but the famous Muslim historian Ibn Khaldun discredited this claim. Al-Hadi was succeeded by his younger brother, Harun al-Rashid.