THE purpose of this note is to present the solar and lunar theory developed by the Damascene astronomer, Ibn ash-Shatir (I304-I375/6 A.D.) 1 in his Kitdb Nihdyat as-Suil fi TashTh al-UEul (A Text of Final Inquiry in Amendig the Elements). Since he dispenses completely with the Ptolemaic eccentric deferent and introduces a second epicycle, both his solar and lunar models are non-Ptolemaic. What is of most interest, however, is that his lunar theory, except for trivial differences in parameters, is identical with that of CoperniCUS (I473-I543). Ptolemy assumed a circular path for the sun, whereas the orbit of Ibn ashShatir's sun deviates slightly from circular motion. The major fault of the Ptolemaic lunar model is in its exaggeration of the variation in lunar distance. The major Copernican contribution to the lunar theory lies in the elimination of this Ptolemaic fault. Five copies of Ibn ash-Shatir's work are known to exist, four of which are at the Bodleian Library. They are MSS Marsh I39, Marsh 290, Marsh 50I, and Hunt 547. The fifth copy is at Leiden, Arabic MS iiI6.3 In the preparation of this paper a microfilm of the first of the above-mentioned copies was used, made available through the courtesy of the Keeper of Oriental Books at the Bodleian. This manuscript of sixty-four folios was copied in 768 A.H. (1366 A.D.), i.e., within the lifetime of the author. In the introduction Ibn ash-Shatir claims that in his treatise he is presenting a planetary theory of finest achievement, and that he has traced and explained all astronomical uncertainties in his Ta'liq al-Arfdd (Comments on Observations). Unfortunately, this work is apparently non-extant. According to our source the inventor's name is Abui'l-Hasan 'All ibn Ibrdhim ibn Mahmalain al-Humam ibn Muhammad ibn Ibrahlm 'Abdur-Rahman alAnsari. Other versions are: Abui'l-Hasan 'All bin Ibrahim bin Muhammad al-Mut'im al-Ansari,4 and 'Ala' ud-Din 'Ali bin Ibrihim Muhammad. In all