This is the first volume of a new trilogy, which will deal with that part of the "Shif?'" which concerns physics and natural philosophy, in Latin the "Liber primus naturalium," One part of the "Liber primus naturalium," which was translated into Latin towards the end of the 12th century, gave rise to the "Tractatus primus de causis et principiis naturalium" and to the "Tractatus secundus de motu et consimilibus," whilst another part translated towards the end of the 13th century produced a "Tractatus tertius de his quae habent naturalia ex hoc quod habent quantitatem," The "Tractatus primus de causis et principiis naturalium," now published, contains like all the other volumes in the series, a doctrinal introduction by Professor G. Verbeke, and an historical and critical apparatus, all prepared by Simone van Riet. The Arabic-Latin and Latin-Arabic lexica will be published separately in a single volume, after publication of the three "Tractatus" has been completed.