This thesis aims to bring to wider attention the work of the Parisian theologian and philosopher Jean-Yves Lacoste (part of the so-called ‘theological turn’ in French phenomenology). Lacoste (whose most recent work, Etre en Danger (2011), articulates what he describes as a ‘phenomenology of the spiritual life’), has previously published monographs in the phenomenology of liturgy (Expérience et l’absolu: Questions disputées sur l'humanité de l'homme, 1994; ET: Experience and the Absolute: Disputed Questions on the Humanity of Man, 2004); hope and eschatology (Note sur le temps: essai sur les raisons de la mémoire et de l'espérance, 1990); philosophy and aesthetics (Le monde et l'absence d'oeuvre, 2000); and phenomenology and theology (Présence et parousie, 2006; Phénoménalité de Dieu, 2008). As a phenomenologist Lacoste is concerned with investigating the human aptitude for experience; as theologian Lacoste is interested in humanity’s potential for a relationship with the divine, what he terms the ‘liturgical relationship’ (where ‘liturgical’ implies more than simply worship writ large but refers instead to a specific anthropology, that of an existence lived and conducted ‘before God’, coram Deo). Beginning from the proposition that prayer is a theme that occurs throughout Lacoste’s writing, the dissertation employs that as a heuristic through which to view, interpret and critique his thought by offering a thematic study of prayer as it appears in his published works. It will look at issues that impact upon the ‘spiritual life’ such as boredom and fatigue, and include the following topics: ambiguity, rumour and the absurd; utopia and fantasy; body, flesh and spirit; silence; time, anarchy and flux. The dissertation is, in part, also an answer to the question as to what kind of theology might be written in response to and in dialogue with Lacoste, by examining some previously overlooked themes in and influences upon his work.