Leontius Of Byzantium (485-543) was a Byzantine monk and theologian who provided a breakthrough of terminology in the 6th-century Christological controversy over the mode of union of Christ's human nature with his divinity. He did so through his introduction of Aristotelian logical categories and Neoplatonic psychology into Christian speculative theology. His work initiated the later intellectual development of Christian theology throughout medieval culture. Brian E. Daley provides translation and commentary on the six theological works associated with the name of Leontius of Byzantium. The critical text and facing-page translation help make these works more accessible than ever before and provide a reliable textual apparatus for furture scholarship of this key writing.