The Paulicians were perhaps the most curious threat to imperil the Roman Empire in the east. Their early history describes a reclusive and vulnerable community wandering throughout eastern Anatolia, yet two bouts of state-sponsored persecution during the ninth century sparked a militarised uprising that thrust this heretical menace onto the regional stage. At first, they raided the empire in concert with the emirates of Melitene and Tarsus, but even when Islamic support collapsed, they retained the strength to strike deep into Roman territory on their own. They were at the height of their power when the most important witness to the movement, Peter the Sicilian, travelled to their stronghold of Tephrike to negotiate a prisoner exchange on behalf of Basil I. This mission triggered the composition of an unusual collection of works, including an extended history of the Paulicians, and three sermons and florilegia that assail the tenets of their heresy. By providing a full English translation of this collection for the first time, this volume introduces and examines these works, while shedding light on the authorship, authenticity, and reliability of an oeuvre that has often provoked controversy.