What really is Christianity? If all the religious packaging in which it is wrapped were removed, what would remain? These were Bonhoeffer's questions, and they must be ours today--even more urgently! For in many quarters Christianity is being so narrowly identified with some of its parts, cultural associations, and past ambitions that like all militant religion, it represents a threat to the planetary future. We may no longer speak clearly of the essence of Christianity, as von Harnack and other nineteenth-century thinkers did; but perhaps we may still have a sufficiently shared sense of the kerygmatic core of this faith to be able, in the face of these misrepresentations of it, to say what Christianity is not.