Fundamental knowledge of the different Christian churches and denominations is indispensable both for theological studies and for the study of Christianity from the perspective of religious studies. It is needed for practical ecclesiastical work as well as for Christian education. Ulrich H. J. Kortners book not only gives an overview of the major trends of Christianity and its churches but also provides fundamental information on Christian ecumenism, its history and current development, including the relationship with Judaism and the other religions, and the state of the discussion on different models of unity of the churches. Thus, it also touches questions of a ecumenical theology.