The effectiveness of worship and prayer was a principle concern of the Franks and took a central position in their interpretation and design of the Christian religion. The Carolingians in particular are known for the way they accentuated a correct practice of worship in order to further the effectiveness of the Eucharistic liturgy and of prayer. This chapter focuses on the Franks' attitude towards sacred language and addresses the question of to what extent their concern with the effectiveness of the religious ritual is visible in their liturgical books. Since the Carolingians were not the first to focus on the effectus of liturgical prayer, it draws a longer line, starting in the early eighth century. It compares a liturgical book from this period with a source dated to the period of Charlemagne's reign.