Authenticity is a value difficult to define but impossible to ignore in contemporary life. The desire for authentic experience pervades art, music, food, dating, marketing, and politics. Worship is no exception: Vatican documents, megachurch websites, pastors, and liturgy planners all make competing claims to offer the genuine article. But what makes liturgy authentic? What distinguishes real celebration from artificial spectacle, heartfelt prayer from empty ritualism, a living tradition from both stagnation and gimmickry? Can today's Christians perform the liturgy so that it is not a mere performance but a sincere offering of their whole selves? In this book, Nathaniel Marx argues that the defining characteristic of authentic liturgy is harmony. Authentic liturgy happens when the minds of participants are in tune with their voices. The call for worshipers to harmonize their inward and outward offerings of prayer is discernible in the Bible, in the history of Christian prayer, and in diverse efforts to invigorate communal worship today. Marx's argument unfolds the meaning of this call to authentic worship through a provocative and wide-ranging study incorporating scriptural exegesis, liturgical history, anthropology of ritual, and philosophy of action. He argues that authenticity is not a modern buzzword but an ancient virtue essential to worshiping in a spirit of communion.