The phenomenon of mutualism—of mutually beneficial cooperation between organisms of different species—has come to a remarkable new prominence in the study of biology. While it does not displace competition, it offers an enlarged, even transformed, picture of the relationships between organisms. The collection of essays in this edition of Theology and Science are presented out of the conviction that today’s flourishing study of mutualism represents a highly significant development in our understanding of biology, which theologians—and others in the arts and humanities—have yet fully to take on board. The aim for this edition of Theology and Science is to provoke theological discussion. As part of that, the present paper sets the scene, with a board scientific survey of mutualism as a biological theme.