In response to many requests for a book descriptive and explanatory of the Gregorian Mass chants, the monks of St. John's Abbey, Collegeville, Minn., undertook the translation from the German of Dom Johner's work under the above title. In the foreword the author indicates the scope of his work. He writes: "The present work is intended chiefly to serve as an aid to the prayerful rendition of the variable chanted parts of the Mass. At the same time it aims to be a guide for the worthy and artistic rendition of those chants which have been handed down to us from an age of strong faith and noble taste." Chant is essentially a form of worship offered by the faithful and as such is an integral part of the liturgy. It is intimately connected with the very source of all Liturgy, the Eucharistic Sacrifice, and attempts to interpret and express in music the sentiments which the text expresses in words. Individual consideration is given to the texts of the Introit, Gradual, Alleluia-verse, Tract, Sequence, Offertory, and Communion. These texts are given in Latin and in English, and are arranged in parallel columns. They are studied in their historical and liturgical setting, and their sentiments of joy and sorrow, hope and fear, gratitude and penance, are pointed out and developed. In this sense also the intimate relationship existing between these various texts is indicated; all are integrated into a unified whole and referred to the life of Christ and His Church. Following this short meditation, the author analyses the musical score accompanying the text, and attempts to show how Gregorian Chant interprets these various sentiments and gives adequate expression to them in short, how Gregorian Chant is the prefect yet simple medium of translating religious emotion into the language of music. An indispensable condition for the intelligent use of this book as a guide Jor interpretation is the simultaneous use of the Vatican Gradual, since musical notation has not been included in the present work. However, only a minimum and very elementary knowledge of Gregorian Chant is necessary for the fruitful use and understanding of the book. Further knowledge is given in a very significant Introduction, which describes the structure and expressiveness of the variable Mass Chants. The original German, as also the English manuscript, have been made the basis for a very successful summer school course in the study of Gregorian Chant. The book might adequately be described as "a study in the appreciation of Gregorian Chant."