A Fellowship of Baptism is a critical rereading of Karl Barth's ecclesiology, arguing that reading his ecclesiology through the lens of his mature view of baptism best enables one to understand Barth's view of the church. Barth's insistence on believer's baptism is connected to the free-church ecclesiology he develops in the Church Dogmatics. The church, for Barth, is a gathered, concrete community formed by the Holy Spirit. The result of believer's baptism should be a community that is free from cultural and political control so that it can serve the world and witness to it. At the same time, questions are raised about Barth's rejection of the sacramental nature of baptism and the implications this has for ecclesiology. The strengths of believer's baptism and the weakness of his non-sacramental view are both seen in his writings on the church and are brought into conversation with one another. Reading Barth's ecclesiology and doctrine of baptism together helps to show the interdependence of baptism and ecclesiology in Barth as well as in all church teaching and practice.