In editing the book for an English audience I have slightly enlarged the index and added a list of New Testament passages referred to. Wherever a German or French book cited by the author has appeared in an English dress, the corresponding reference has been subjoined. Also, in deference to certain suggestions received by the publishers, I have added, wherever it has been advisable to do so, English versions of the Greek and Latin passages which form so valuable and characteristic a feature of Dr Harnack's historical discussions. It is hoped that the work may be thus rendered more intelligible and inviting than ever to that, wider audience whose interest in early Christianity is allied to little or no Greek and Latin. The first edition of this translation was issued in 1904 — 1905, and the first volume is now out of print. Meanwhile, Dr Harnack published, in 1906, a new edition of the original in two volumes, which has been so thoroughly revised and enlarged that, with its additions and omissions, it forms practically a new work. His own preface to the second edition gives no adequate idea of the care and skill with which nearly every page has been gone over in order to fill up any gaps and bring the work up to date. The present version has been made directly from this edition. I have taken the opportunity of correcting some misprints which crept into the first edition of my translation, and it is hoped that English readers will now be able to find easy access to this standard history in its final form.