Prayer is a cornerstone of religious life, practiced by over 50% of Americans on a daily basis(1). Prayer practices foster a variety of contemplative experiences with deep personal and cultural significance(2,3). For example, evangelical or charismatic Christians—who make up nearly 10% of the global population(4)—often report seeing visions that they experience as originating from an external, divine source. Both researchers and practitioners have attributed these events to the practice of prayer(5). However, despite the widespread occurrence of such religious experiences, the cognitive mechanisms of prayer remain largely unknown. Ethnographic research suggests that specific forms of Christian prayer nurture vivid religious experiences, in part by enhancing the capacity for mental imagery(6,7). Here we propose a longitudinal experiment to ground these ethnographic insights at the level of cognitive mechanisms. We will randomize 60 healthy Christians to four weeks of either imagination-based prayer or a Bible-study active control. We will measure changes in religious experience and mental imagery using a combination of first-person (questionnaires and thought sampling task), second-person (phenomenological interviews), and third-person (behavioral psychophysics) methods. Our project will extend scientific research on meditation into the domain of Christian spirituality while elucidating the role of mental imagery in contemplative practice.