From the early 1930s; the Christian witness for peace was one of Dietrich Bonhoeffer's most consuming preoccupations; both intellectually and in action. In this, far from being a lone voice, he was but one of numerous Christians in many countries for whom the cause of peace, set against the tragic experience of 1914-18 and the resurgence of nationalism and militarism in the 1930s, was paramount. To isolate Bonhoeffer from the wider movement in which he took part, casting him in the role of sole prophet or hero, would not only be historically unreal; it would also obstruct the view of his distinctive contribution. It was in his sharp theological interaction with his partners in ecumenical peace-work, no less than in his opposition to the menacing political demons of his time, that his critical - and continuing - significance is to be seen. This chapter will concentrate on Bonhoeffer's theological contribution during the critical years 1932-4.