Abū Muḥammad ʿAbd Allāh ibn Yūsuf (Arabic: أبو محمد عبد الله بن يوسف; 1151–1171), better known by his regnal name al-ʿĀḍid li-Dīn Allāh (Arabic: العاضد لدين الله, lit. 'Strengthener of God's Faith'), was the fourteenth and last caliph of the Fatimid dynasty, and the 24th imam of Hafizi Isma'ilism, reigning from 1160 to 1171.

Coming to the throne as a child, al-Adid spent his reign as a puppet in the hands of various strongmen who occupied the vizierate, and was a mostly helpless bystander to the gradual collapse of the Fatimid Caliphate. In the course of his reign, both the Crusader Kingdom of Jerusalem and the Sunni Syrian ruler Nur al-Din availed themselves of the power struggles in Cairo and the enfeeblement of the Fatimid state to advance their own designs on the country. For a while, the vizier Shawar tried to play both sides off against one another, but in January 1169, Nur al-Din's general Shirkuh finally managed to overthrow Shawar and occupy Cairo. Appointed to the vizierate, Shirkuh died shortly after and was followed by his nephew, Saladin, who not only consolidated his hold over Egypt, but proceeded to gradually dismantle the Fatimid regime. Fatimid loyalists in the army were purged, and Isma'ilism was abolished as the state religion in favour of Sunni Islam, culminating in the official proclamation of Abbasid suzerainty in September 1171. Al-Adid died a few days later. His family was placed under house arrest, and Isma'ilism persecuted by Saladin's new Ayyubid regime, so that within a century after the fall of the Fatimid regime it had almost disappeared in Egypt.