This is the first English translation of a major work by Rupert of Deutz, arguably the most prolific Christian author since Augustine. During his lifetime, which spanned the eleventh and twelfth centuries, Rupert engaged in controversies on the Eucharist and on predestination and composed works on the Trinity, salvation in Christ, and other major theological topics. An ardent defender of a monastic theology that focused on the interpretation of Scripture and the liturgy, Rupert is well known also for his distinctive hermeneutical approach to the Bible. His Commentary on the Songs of Songs builds on the long Hebrew-Christian tradition of allegorical interpretation of this Old Testament book but adds a radically original dimension to it: it interprets the text as a dialogue between Jesus and Mary and unfolds in this context a novel approach to Mary, who is presented as the teacher of the apostles and assumed to have participated in the Apostolic Council, described in Acts 15. Rupert has prefaced his commentary with a letter to Thietmar, bishop of Verden (in northern Germany), as well as a prologue in which he reflects on his experience of being called to perform this exegetical task. The complete translation by Jieon Kim and Vittorio Hösle of this major work (up to now translated only into German) is preceded by an introduction that discusses Rupert's life and works, as well as the history of the interpretation of the Song of Songs, and offers hermeneutical reflections on Rupert's methodology.