This paper traces the origins and subsequent use of the concepts of 'organic union' and 'reconciled diversity' as alternative descriptions of the visible unity of the Church and the method and goal of ecumenism, with special reference to the documents of the World Council of Churches and a select number of related texts emanating from theological dialogue at a world level. The paper argues: (1) that each of these concepts preserves valuable insights into the unity and diversity of the Church; (2) that the corresponding approaches to inter-church relations and dialogue need not be incompatible as ecumenical method; (3) but that 'reconciled diversity', as it is usually described, is only a temporary state on the way to 'organic union' and not itself a sufficient expression of the full visible unity of the Church. This paper traces the origins and subsequent use of the concepts of 'organic union' and 'reconciled diversity' as alternative descriptions of the visible unity of the Church and the method and goal of ecumenism, with special reference to the documents of the World Council of Churches and a select number of related texts emanating from theological dialogue at a world level. The paper argues: (1) that each of these concepts preserves valuable insights into the unity and diversity of the Church; (2) that the corresponding approaches to inter-church relations and dialogue need not be incompatible as ecumenical method; (3) but that 'reconciled diversity', as it is usually described, is only a temporary state on the way to 'organic union' and not itself a sufficient expression of the full visible unity of the Church.