This chapter considers why contemporary analytic philosophers of religion have neglected liturgy and focused almost all of their attention on religious belief. Following Descartes, reflections on mental activity and the mind have been central in modern philosophy. But that has not prevented the emergence of philosophy of art, philosophy of language, and political philosophy, none of which deal with mental activity or the mind. So why not philosophy of liturgy? Several explanations are considered; but none is found to be fully satisfactory. The Introduction concludes with an explanation of how the subsequent discussion relates to liturgical theology and to anthropological ritual studies.