St. Basil was one of the most popular of the Greek Fathers amongst the Syrian churches, and his De Spiritu Sancto was twice translated into Syriac. The first version, made in the late fourth/early fifth centuries, survives the three manuscripts of the fifth-seventh centuries and is edited and translated here for the first time. It is a paraphrastic text and so is of theological interest in its own right. Its biblical citations are also noteworthy. The second translation, made in the seventh century, survives only in fragments and these have been collected from florilegia manuscripts and edited in parallel with the Greek text. Introductions to the two volumes explore the Syriac manuscript traditions of this work and their significance, and investigate St. Basil's contacts with Syriac-speaking Christians and the theology of the first Syriac version. Unusually, a detailed orthographic index of textual variants is also included.