Abū Bakr ʿAbd al-Raḥmān b. Kaysān al- Aṣamm (d. 200/816 or 201/817) was an important Basran theologian and exegete, commonly, though with some reservation, considered a Muʿtazilī. Information about his life is scarce. He was born in Basra, where he spent most of his life. During his youth he served, together with other mutakallimūn (theologians), as an assistant to Maʿmar Abū l-Ashʿath (second half of the second/eigthth century; van Ess, TG , 2:37-9), a Basran physician whom al-Jāḥiẓ (d. 255/868-869) called "