The present English edition is translated from the third French edition (Paris, 1911), the difference consisting in a series of corrections of details. The most note-worthy among them are due to the suggestions of that excellent liturgist, M. Atwell Baylay, whom I take pleasure in thanking for the friendly care and attention he has bestowed on the English translation. The "conclusion" of the French edition has been omitted, and a chapter on the reform of Pius X has been added in its place. No one would have accepted the idea of a history of the Roman Breviary that should have left out the conclusion which the Holy See has just given to the projects of Benedict XIV by the Bull DivinuAfflatu of November 1, 1911. In writing these additional pages, I have had great satisfaction in finding, in all that the papal reform restores, the fulfillment of those desires my book first gave respectful expression to twenty years ago. (Author's preface to the new english edition)