IMPORTANT as was for centuries the part played by the interdict in the history of both church and state, no book has hitherto been devoted to it. Late in the sixteenth century the French jurist Pierre Pithou attempted a survey of its history in his essay De l'ongine et du progres des Interdicts ecclesiastiques; but this, though able, is only a sketch. In 1869 the German canonist Franz Kober published in three successive issues of the Archiv fur katholisches Kirchenrecht a careful study entitled "Das Interdict." While rich in information regarding the history and use of the interdict, this deals mainly with its place in ecclesiastical law. In 1897 a young American scholar, Arthur C. Howland, submitted for the doctorate at the University of Pennsylvania a thesis on "The Interdict, its Rise and Development to the Pontificate of Alexander III," i. e., to 1159. This thesis has never been printed; but in 1899 Dr. Howland read before the American Historical Association a paper based upon it-', The Origin of the Local Interdict - which was published in the Association's report for that year. It narrates the story of the interdict to 1031. Excepting pamphlets purely polemic, like those called forth by the Venetian interdict of 1606, and narratives devoted to single episodes, these few studies form the entire monographic literature of the subject. The present essay, while aspiring to serve as a convenient introduction to a knowledge of the interdict, attempts no exhaustive treatment. To the history of the interdict its fresh contribution is only a sifting and use of the materials for the time of Pope Innocent III. Nor is it meant to be a study of the canonical law relating to the discipline-a theme adequately treated by the canonists. Its aim is to show the actual use and effects of the interdict; and by" the interdict" it for the most part means only what has been currently known in history by that name-the comprehensive territorial measure known to canonists as the" local general interdict," and not unhappily defined by an American newspaper, in a recent case of its employment, as " a general ecclesiastical strike ."