As the Holy Sacrifice of the Mass is the centre of Catholic worship and life, a more profound knowledge of the Mass is considered essential and most desirable for all the faithful, but especially for the priest. Although literature on this subject is rather abundant, the present volume, which has been drawn from every available source at the Author's command, may not be deemed superfluous. Its object is, in the main, both practical and ascetical: to appeal not only to the understanding, but also to inflame the heart and to move the will. The selection and the treatment of the matter have necessarily been directed to this object. As it is not our intention to present a purely scientific and exhaustive treatise on the Eucharistic Sacrifice, but to build, upon the foundation of scientific studies and inferences, a work useful and practical for the clergy, certain questions of scientific and historic nature may receive scarcely more than a brief and passing mention. Denis the Carthusian - "In this writing it was not my intention in expounding the words of the Mass as devoutly as I could, to raise any question or touch on anything but what might move the heart and excite to devotion." Therefore all polemical, critical quotations and statements open to contradiction have, as much as possible, been avoided. In disputed points we have always seriously and carefully weighed the reasons pro and con; but in the book itself we have merely stated what appeared to us the most solidly grounded. As edification and devotion must at all times rest on theological truth and emanate from it, it became necessary to present the Dogma and Rite of the Eucharistic Sacrifice clearly, thoroughly and correctly, according to the spirit and intention of the Church; thus only do the ascetical considerations and applications find a solid foundation to rest on. "For without truth, piety is feeble; and without piety, truth is sterile and void." (Suarez) In the explanation of the Rite we have strictly adhered to the words and actions of the liturgical formulae, endeavoring at the same time, in accordance with approved ecclesiastical tradition, to avoid as far as possible all subjectivism and artificiality. A correct and clear understanding as well as frequent consideration of the profound and mystical Rite of the Mass, will, in all probability, be the best means to enable the priest to refrain from a thoughtless, habitual mannerism, and lead him' to celebrate the adorable mysteries of the Altar with becoming attention, devotion, and reverence. The priest who studies this book will, moreover, find manifold reasoning and argument wherewith to direct the faithful according to their capacity in the proper understanding of the Di\-ine Sacrifice and in their fervent recourse to the Eucharistic fouiltain of grace. The authorities of the Church have often impressed upon pastors, that this is a chief duty of directors of souls, for the conscientious discharge of which they shall have to render an account before God. Although this volume is principally intended for the use of the clergy, it has been so arranged that the more highly cultured of the laity may also peruse it with profit.