Book excerpt: In Christ Existing as Community, Michael Mawson recovers and clarifies the German theologian Dietrich Bonhoeffer's early and important work on ecclesiology, focusing especially on his doctoral dissertation Sanctorum Communio. Despite occasional pronouncements of the importance of this dissertation, it has still received only limited scholarly attention. Mawson demonstrates how Bonhoeffer draws upon and reworks social theory in order to develop an account of the church as a reality of God's revelation and a concrete human community. On this basis Mawson concludes that Bonhoeffer's ecclesiology has ongoing significance for contemporary debates in theology and Christian ethics.