This book provides a metaethical analysis of the responsibility ethics of H. Richard Niebuhr and Emmanuel Levinas. It probes the plausibility of their ethical theories by revealing and clarifying some conceptual difficulties and logical inconsistencies found in their ethics in order to advance current scholarship in responsibility ethics. In addition to illumining various theological and philosophical backgrounds of their ethics, this study offers a critical reflection on some of the major metaethical topics relevant to each thinker.