Scholars laud and critique Dietrich Bonhoeffer’s ethic for its utilization of a Grenzfall, or borderline case. This essay examines Bonhoeffer’s conception of the borderline case in conversation with prior uses of this term by Carl Schmitt and Karl Jaspers, and with later uses by Karl Barth, John Howard Yoder, and Larry Rasmussen. Bonhoeffer’s borderline cases share features with these interlocutors, but the meaning he gives the term is not finally identical with any of their conceptions. Furthermore, Bonhoeffer’s manuscripts addressing »Natural Life«, »Responsible Life«, and »The ›Ethical‹ and the ›Christian‹ as a Topic« demonstrate development in his own understanding of the borderline case. Throughout his Ethics, however, the borderline case remains an uncommon conflict between moral norms. The essay concludes proposing a modification of Bonhoeffer’s borderline case by drawing upon Robin Lovin’s recognition of the multiplication of mandates and the pervasiveness of moral conflicts.