 To some extent, scholars disagree about the role of the Greek sources in Arabic and Islamic philosophy (henceforth falsafa, the Arabic loan word for  φιλοσοφία).[1]  While acknowledging the existence of a Greek heritage, those who consider the Qur’an and the Islamic tradition as the main source of inspiration for falsafa claim that the latter did not arise from the encounter of learned Muslims with the Greek philosophical heritage: instead, according to them falsafa stemmed from the Qur’anic hikma (“wisdom”). As a consequence, the Greek texts in translation are conceived of as instruments for the philosophers to perform the task of seeking  wisdom.[2]  However, most scholars frequently side with the opinion that what gave rise to the intellectual tradition of falsafa was the so-called movement of translation from  Greek.[3]  This entry will not discuss the issue, let alone try to settle it: it will limit itself to present the philosophical Greek sources made available from the beginnings of the translations into Arabic to the end of the 10th century. The reason for focusing on the various stages of the assimilation of the Greek heritage, instead of taking into account one by one all the works by Plato, Aristotle etc. known to Arabic  readers,[4]  is that it is useful to get an idea of what was translated at different times. As a matter of fact, a living interplay took place, especially in the formative period of falsafa, between the doctrines of the philosophers writing in Arabic and the Greek sources made available. Of momentous importance for the development of falsafa was the simultaneous translation of Aristotle’s Metaphysics and De Caelo, some writings by Alexander of Aphrodisias (most of them of a cosmological nature), Plotinus’ Enneads IV–VI, and Elements of Theology by Proclus. Al-Kindi, the first faylasuf, initiated the incorporation of the Aristotelian, Peripatetic and Neoplatonic doctrines; at the same time, he reproduced them in his philosophical works. Later on, the knowledge of the complete Aristotelian corpus provided by another generation of translators, without altering substantially this picture, produced a different approach. The Aristotelian science as a systematic whole, ruled by demonstration and made available together with Euclid, Ptolemy, Hippocrates and Galen, paved the way for al-Farabi to build up the project of a curriculum of higher education, which was meant to subsume the native Islamic sciences in the broader system of the liberal arts and philosophical sciences. Both the cross-pollination of the Aristotelian and Neoplatonic traditions of the Kindian age, and the rise of a complete system of rational sciences in the light of Farabi’s educational syllabus of the philosopher-king, lie in the background of Avicenna’s program to provide the summa of demonstrative science—from logic to philosophical theology—as a necessary step for the soul to return to its origin, the intelligible realm (Endress 2006). When Averroes, two centuries after the end of the age of the translations, resumed the project of building up the demonstrative science as a systematic whole, he had recourse to the Greek sources in Arabic translation which were available in the Muslim West, mostly Aristotle and his  commentators.[5]