The coming together of people of diverse religions to plan or reflect upon a common action or venture, and to consider, let alone engage in, an act of shared spiritual experience – such as interreligious prayer – is something comparatively novel and relatively rare. Yet the impetus for acts of inter-faith prayer, worship, or other liturgically shared acts, is increasing as more and more experiences of cross-religion engagement and dialogical encounter occur, and as communities encompassing religious diversity address issues in common, or respond to crises that affect all. In some corners of the globe this is already very much the case; for others it is only just emerging into view on the horizon of possibility. In this paper I explore the question of interreligious prayer arising from my involvement in a joint World Council of Churches and Vatican Study undertaken during the 1990s. The questions which lay behind this co-operative venture remain, of course, live ones today and require continual reflection and fresh thinking. When the natural human response is to pray, and the context of that response is multi-religious, what can we do together? How can we do it? Indeed, ought we to do it? And if we do, on what basis may we proceed? What justification can we give in respect of our own faith? What are the issues to be addressed? How, if at all, may they be resolved?