No historical study of current issues—politics or social science or theology—can far proceed without bringing the student face to face with the principles asserted by the Reformation of the Sixteenth Century and its great leader, Martin Luther. He has had many critics and many champions, but neither his critics nor his champions feel that the last word concerning him has been spoken, for scarcely a year passes that does not witness the publication of a new biography. Had Luther been nothing more than a man of his own time and his own nation the task of estimating him would long since have been completed. A few exhaustive treatises would have answered all demands. But the Catalogue of the British Museum, published in 1894, contains over two hundred folio pages, averaging about thirty-five titles to the page, of books and pamphlets written either by or about him, that have been gathered into this single collection, in a land foreign to the sphere of his labors, and this list has been greatly augmented since 1894. Above all other historical characters that have appeared since the first years of Christianity, he is a man of the present day no less than of the day in which he lived. But Luther can be properly known and estimated only when he is allowed to speak for himself. He should be seen not through the eyes of others, but through our own. In order to judge the man we must know all sides of the man, and read the heaviest as well as the lightest of his works, the more scientific and theological as well as the more practical and popular, his informal letters as well as his formal treatises. We must take account of the time of each writing and the circumstances under which it was composed, of the adversaries against whom he was contending, and of the progress which he made in his opinions as time went on. The great fund of primary sources which the historical methods of the last generation have made available should also be laid under contribution to shed light upon his statements and his attitude toward the various questions involved in his life-struggles. As long as a writer can be read only in the language or languages in which he wrote, this necessary closer contact with his personality can be enjoyed only by a very limited circle of advanced scholars. But many of these will be grateful for a translation into their vernacular for more rapid reading, from which they may turn to the standard text when a question of more minute criticism is at stake. Even advanced students appreciate accurately rendered and scholarly annotated translations, by which the range of the leaders of human thought, with whom it is possible for them to be occupied, may be greatly enlarged. Such series of translations as those comprised in the well-edited Ante-Nicene, Nicene and Post-Nicene Libraries of the Fathers have served a most excellent purpose.