That the book now presented to the public may be of service to the teacher and student of ecclesiastical history is my sincere wish. It may easily happen that no one else would make just the same selection of sources here made. But it is probable that the principal documents, those on which the majority would agree and which are most needed by the teacher in his work, are included among those presented. There are, no doubt, slips and defects in a book written at intervals in a teacher’s work. With the kind co-operation of those who detect them, they may be corrected when an opportunity occurs. JOSEPH CULLEN AYER, JR. GENERAL BIBLIOGRAPHICAL NOTE Under each period special collections of available sources are to be found. The student is not given any bibliography of works bearing on the topics, but is referred to the following accessible works of reference of recent date for additional information and bibliographies: _The New Schaff-Herzog Encyclopædia of Religious Knowledge_, edited by S. M. Jackson, New York, 1908-12. _The Catholic Encyclopædia_, New York, 1907-12. _The Encyclopædia Britannica_, eleventh edition, Cambridge, 1910. _The Encyclopædia of Religion and Ethics_, edited by J. Hastings, Edinburgh and New York, 1908 ff. (In course of publication.) For the patristic writers, their lives, works, editions, and other bibliographical matter, see: G. Krüger, _History of Early Christian Literature in the First Three Centuries_, English translation by C. R. Gillett, New York, 1897. Cited as Krüger. B. Bardenhewer, _Patrologie_, Freiburg-i.-B., 1911, English translation of second edition (1901) by T. J. Shahan, St. Louis, 1908. Cited as Bardenhewer. In addition to the encyclopædias the following are indispensable, and should be consulted: Smith and Wace, _Dictionary of Christian Biography_, Literature, Sects and Doctrines, London, 1877-87. (The Condensed Edition of 1911 by no means takes the place of this standard work.) Cited DCB. Smith and Cheetham, _Dictionary of Christian Antiquities_, London, 1875-80. Cited DCA. Advanced students and those capable of using French and German are referred to the following, which have admirable and authoritative articles and ample bibliographies: _Realencyclopædie für protestantische Theologie_, edited by A. Hauck, Leipsic, 1896 _ff._ Two supplementary volumes appeared in 1913. Cited PRE. _Kirchenlexicon oder Encyclopædie der katholischen Theologie und ihrer Hilfswissenschaften_, second edition, by J. Hergenröther und F. Kaulen, Freiburg-i.-B., 1882-1901. Cited KL. _Dictionnaire de Théologie Catholique_, edited by A. Vacant and E. Mangenot, Paris, 1903 _ff._ _Dictionnaire d’Archéologie Chrétienne et de Liturgie_, edited by F. Cabrol, 1903 _ff._ _Dictionnaire d’Histoire et de Géographie Ecclesiastiques_; edited by A. Baudrillart, A. Vogt, and U. Roziès, Paris, 1909 _ff._