Abū al-Fatḥ al-Iṣfahānī, Maḥmūd b. Qāsim b. al-Faḍl (d. after 513/1119) was an Iranian mathematician. Some sources refer to him by the name Muḥammad b. al-Qāsim (Suter, 98; Steinschneider, 184; cf. Qurbānī, 92). It is known that some time around 513/1119 he was in Yazd staying at the court of ʿAlāʾ al-Dawla Abū Kālījār Garshāsp b. ʿAlāʾ al-Dawla Amīr ʿAlī, one of the kings of the Kākūyid dynasty, during which time Abū al-Fatḥ wrote for him (Abū al-Fatḥ, fol. 3a, and last fol.).