The Taktika, ascribed to the hand of the Byzantine emperor Leo VI “the Wise” (886–912), is perhaps one of the best-known middle Byzantine texts of an official or semi-official genre. Presented in the form of a book of guidance for provincial generals, it served as both a statement of imperial authority and power, as well as a reminder of earlier “good practice” and the centrality of the values of a Christian society in the struggle against its enemies. In particular, the Taktika identified Islam, for the first time, as a fundamental threat to the very existence of the Christian Roman Empire and Christianity itself. Yet despite its significance for the history of Byzantine administration, culture, language, and society, no study has ever been devoted to this fascinating text. John Haldon offers the first critical commentary to appear in any language, addressing in detail the many varied subjects touched on in the treatise itself and accompanied by three introductory chapters that examine the context, sources, language, structure and content of the text, as well as the military administration of the empire in Leo’s time.