Translator’s Preface. Although, according to the plan of this “Library,” Commentaries on Holy Scripture are omitted, and the field of selection is thus somewhat lessened, it has been no easy matter to decide which of St. Ambrose’s many treatises should be chosen and which omitted. Obviously the great work on the Faith, De Fide, must be included, and this implied the addition of that on the Holy Spirit. Then the treatise on the Duties of the Clergy, as throwing much light on the ideas of the Fourth Century as to what was expected of ecclesiastics, seemed to claim a place. And after these the difficulty becomes very great. It is unfortunate that the limitations of space do not admit of the inclusion of all the dogmatic and ascetic treatises. Similarly, one would have been glad to insert the addresses on the deaths of the two Emperors Valentinian and Theodosius. More, also, of his letters might well have been added, though, as they have appeared in full in the Oxford “Library of the Fathers,” this is a matter for less regret. As will be seen, I have availed myself of the assistance of my son, the Rev. E. de Romestin, of New College, and of the Rev. H. T. F. Duckworth, of Merton College, each of whom took high honours in the Theological School at Oxford. The work has been carried out under some difficulties, and not the least has been the loss in travelling of a considerable portion of the manuscript, the whole of which had to be translated anew.