Ptolemy (d. ca 170) was perhaps the most famous theoretician of celestial science of his time, up to the Renaissance. Yet al-Kindī (d. ca 870), who was the first philosopher to write in Arabic, seems to have considered him to be a philosopher as well. According to him, the preface to the Almagest “touches upon the noblest topics of philosophy”. But how did Ptolemy see himself? And how do later writers, whether in late antiquity or the Islamicate world, interpret his project? This is the framework within which the chapters of this volume unfold, illuminating Ptolemaic philosophy and its reception, a subject that has remained understudied until very recently. It is supplemented by editions and translations of key texts at issue in Greek and Arabic.