The dissertation explores Karl Barth?s discourse about Mary and Mariology. The chronologically listed Marian textual references in Barth?s literary opus yield a positive answer to the question whether in Karl Barth as a Reformed theologian sufficient material for a dissertation about the Blessed Virgin Mary can be found at all. Chronologically listed Marian passages are also crucially important for easier following and more precise analysis of the development and transformation of Barth?s Marian discourse. Attention is systematically drawn to the figure, place, task and significance of Mary in God?s plan of salvation within Barth?s discourse about Mary and Mariology. Barth?s statements about Mary are located at the junction of his Christological theology. Barth talks about Mary primarily because she is intimately included in the doctrine of the Incarnation. Beside the virgin birth, the divine motherhood of Mary is considered as a fundamental proposition of Christianity in Barth?s Marian discourse. With his energetic defense of the virgin birth of Jesus he declares himself unequivocally in favor of the virginity of Mary in the conception, though he doesn?t confess virginitas in partu et post partum. Barth, however, talks about Mary not only within the thematic circle of the Incarnation, but also in various contexts of constant confrontation with Catholic theology. From the constant dialogue with Catholic theology grows his sharp criticism of Mariology. But Barth takes back the whole criticism of Mariology with the statement that the question of Mariology still hasn?t been worked out and that, from the Reformed side, it must be thought through from the beginning. Is it not the case, then, that in this way there issues from Barth?s Marian discourse a notable impetus for a drawing nearer in ecumenical dialogue between Protestants and the Catholic Church on the question of Mary?