THIS series of Handbooks is designed to meet a need, which, the Editors believe, has been widely felt, and which results in great measure from the predominant importance attached to Dogmatic and Moral Theology in the studies preliminary to the Priesthood. That the first place must of necessity be given to these subjects will not be disputed. But there remains a large outlying field of professional knowledge which is always in danger of being crowded out in the years before ordination, and the practical utility of which may not be fully realised until some experience of the ministry has been gained. It will be the aim of the present series to offer the sort of help which is dictated by such experience, and its developments will be largely guided by the suggestions, past and future, of the Clergy themselves. To provide Textbooks for Dogmatic Treatises is not contemplated-at any rate not at the outset. On the other hand, the pastoral work of the missionary priests will be kept constantly in view, and the series will also deal with those historical and liturgical aspects of Catholic belief and practice which are every day being brought more into prominence. That the needs of English-speaking countries are, in these respects, exceptional, must be manifest to all. In point of treatment it seems desirable that the volumes should be popular rather than scholastic, but the Editors hope that by the selection of writers, fully competent in their special subjects, the information given may always be accurate and abreast of modern research. The kind approval of this scheme by His Grace the Archbishop of Westminster, in whose Diocese these manuals are edited, has suggested that the series should be introduced to the public under the general title of THE WESTMINSTER LIBRARY. It is hoped, however, that contributors may also be found among the distinguished Clergy of Ireland and America, and that the Westminster Library will be representative of Catholic scholarship in all English speaking countries. THIS book is intended to supply information about the history of the Roman liturgy. The dogmatic side of the Mass is discussed by the Bishop of Newport in the same series. The title shows that it is a study of the Roman rite. It is only in the Roman (or Gallican) rite that the Eucharistic service can correctly be called Mass. The chapter about other liturgies and the frequent references to them throughout are meant only to put our Roman Mass in its proper perspective and to illustrate its elements by comparison. In spite of the risk of repetition, the clearest plan seemed to be to discuss first the origin and development of the Mass in general; and then to go through the service as it stands now, adding notes to each prayer and ceremony. The present time is perhaps hardly the most convenient for attempting a history of the Mass. For never before have there been so many or so various theories as to its origin, as to the development of the Canon, the Epiklesis and so on. Where the best authorities differ so widely it would be absurd to pretend to offer a final solution. I have no pretence of supplying a new answer to any of these questions, or even of taking a side finally among theories already proposed. The only reasonable course seems to be to state the chief systems now defended and to leave the reader to make up his own mind. I have however shewn some preference for the main ideas of Dr. Drews and Dr. Baumstark and for certain points advanced by Dr. Buchwald.