I have relied upon a great variety of sources belonging to the various orders in the hierarchy of historical literature; it is happily unnecessary to catalogue these. In some instances I have found other manuals, dealing with portions of my field, of value. In the earlier chapters, Emerton's admirable _Introduction to the Middle Ages_ furnished many suggestions. For later periods, the same may be said of Henderson's careful _Germany in the Middle Ages_ and Schwill's clear and well-proportioned _History of Modern Europe_. For the most recent period, I have made constant use of Andrews' scholarly _Development of Modern Europe_. For England, the manuals of Green and Gardiner have been used. The greater part of the work is, however, the outcome of study of a wide range of standard special treatises dealing with some short period or with a particular phase of European progress. As examples of these, I will mention only Lea's monumental contributions to our knowledge of the jurisprudence of the Church, Rashdall's _History of the Universities in the Middle Ages_, Richter's incomparable _Annalen der Deutschen Geschichte im Mittelalter_, the _Histoire Générale_, and the well-known works of Luchaire, Voigt, Hefele, Bezold, Janssen, Levasseur, Creighton, Pastor. In some cases, as in the opening of the Renaissance, the Lutheran Revolt, and the French Revolution, I have been able to form my opinions to some extent from first-hand material. My friends and colleagues have exhibited a generous interest in my enterprise, of which I have taken constant advantage. Professor E.H. Castle of Teachers College, Miss Ellen S. Davison, Dr. William R. Shepherd, and Dr. James T. Shotwell of the historical department of Columbia University, have very kindly read part of my manuscript. The proof has been revised by my colleague, Professor William A. Dunning, Professor Edward P. Cheyney of the University of Pennsylvania, Dr. Ernest F. Henderson, and by Professor Dana C. Munro of the University of Wisconsin. To all of these I am much indebted. Both in the arduous preparation of the manuscript and in the reading of the proof my wife has been my constant companion, and to her the volume owes innumerable rectifications in arrangement and diction. I would also add a word of gratitude to my publishers for their hearty coöperation in their important part of the undertaking.