Dietrich Bonhoeffer (1906-1945) is the worldwide most renowned German theologian of the 20th century. Before his assassination by the National Socialist state he wrote in prison letters and papers which are a theological and spiritual legacy of his work. Bonhoeffer discusses intensely the challenges for Christianity brought by totalitarianism. At the same time he gives ground-breaking impulses for a Christianity of the future which are fascinating and challenging until today. The commentary puts Bonhoeffer's reflections in relation to his theological development and its intellectual sources. It is suitable as a first introduction to the theologian Dietrich Bonhoeffer, for the teaching in upper secondary classes, and for the self-study of the interested reader.