'Isa ibn Musa ibn Muhammad ibn Ali ibn Abdallah ibn al-Abbas (died 783/4) was a nephew of the first two Abbassid Caliphs, as-Saffah (r. 750–754) and al-Mansur (r. 754–775), and for a long time heir-apparent of the Caliphate, until he was superseded by al-Mansur's son al-Mahdi (r. 775–785). Nevertheless, in 764/5 he was pressured into ceding his place in the succession to al-Mansur's son, al-Mahdi, and again in 776, when al-Mahdi forced him to renounce his succession in favour of al-Mahdi's son Musa al-Hadi (r. 785–786).