The problem with which this investigation is concerned is that of comparing the medieval musical traditions of two of the world's most influential religions. The similarities are discussed in two major categories: the comparison of liturgical texts and ritual, and the comparison of the music appearing in each ritual. This study has one main purpose. That purpose is to demonstrate how, through musical traditions, each religion has developed through the influence of the other. Samples of the liturgies from the musical portions of the services were obtained from prayer books and references dealing with those religions. Investigations of English translations from the Latin and Hebrew revealed a close identity between the two, not only in scriptural uses, but also in prayers and responses. Musical examples demonstrating similar elements in Hebrew and Christian worship were found in the extensive research of A. Z. Idelsohn and Eric Werner. Due to the dispersal of world Jewry, the best examples of Hebrew medieval music were obtained from the most isolated Jewish communities, such as those of Yemen, Musical similarities included modes, melodic formulas, and hymns and songs. This report concludes that the musical portions of the services of Christianity and Judaism in the Middle Ages were strikingly similar, and their subsequent musical development was strongly influenced by their coexistence.