The Mu'tazilites were an important theological school of early Islam, which flourished in Basra and later Baghdad in the 2nd century AH. The theologians of this tradition formulated a set of principles regarding the oneness of God, divine justice, promises and oaths, the middle position of the sinner, and enjoining good; accounts of its beginnings are not consistent in historical sources.

The Mu'tazilites gained court influence during the Abbasid Caliphate and then lost their institutional status, but their arguments influenced the history of Islamic theology. Today, the title is more commonly used for a historical intellectual tradition and should not be confused with a contemporary branch with a unified membership.