The authors provide us with the Syriac text together with a translation of part of the controversy between the patriarchs Peter and Damian from the end of the sixth century, over alleged "tritheism" with which Peter of Callinicum was charged by his "Sobellianizing" opponents. With the publication and translation of this dossier we have a window opened on the debates that developed between Chalcedonian and non-Chalcedonian churchmen and theologians. Illuminating accounts are offered of the life and writings of Peter of Callinicum, the anti-Tritheist dossier, and the Tritheist controversy up to 586 together with a brief summary of "the Tritheist Doctrine" and then an account of the controversy between Peter and Damian.