Book excerpt: The author has tried to define liturgical theology, noting especially its progress beyond liturgics, the study and comparison of texts, and showing how the dynamic realism of the Eucharistic liturgy has been often obscured in popular liturgical piety. These themes are developed in reference to the Ordo or shape of worship as it evolved in the Orthodox Church, from the very earliest years down to the 'crystallization' of worship in Byzantine Orthodoxy in the ninth-twelfth centuries.