Euthymios Zigabenus was an important writer and thinker of the 12th century, yet little is known of his life or works. He is most well known for his treatise, the Panoplia Dogmatica, which lists and describes various heresies known to Euthymios. Most notable among these heresies is the Bogomilian heresy because the Panopllia serves as one of the only sources for information about this sect, and Euthymios’s account comes from his own interaction with its adherents. Jacob Wickert offers here one of the most thorough descriptions of Euthymios and his work ever produced. Wickert begins with an introduction to the life of Euthymios with careful attention to his relationship with Emperor Alexios, who requested that Euthymios write the Panoplia. Wickert describes the basic structure of the Panoplia and goes on to provide a list of the known patristic sources that Euthymios cites in the work. Wickert proceeds with an overview of the Panoplia, providing a detailed account of the progression of thought and the key ideas presented. Wickert concludes by offering an assessment of the value of the Panoplia and concludes that it has been overlooked as an important historical document chronicling Christianity in the 12th century.