Yves R. Simon (1903-1961) is often considered one of this century’s greatest students of the virtue of practical wisdom. Simon’s interest in this virtue ranged from ultimate theoretical and foundational concerns, such as the relationship between practical knowledge and science, to the most concrete and immediate questions regarding the role of practical wisdom in personal and social decision-making. These concerns occupied Simon from his earliest published writing to the final notes and correspondence he was working on at the moment of his untimely death. Throughout his life, practical wisdom and its related philosophical ramifications emerge time and again at critical junctures, throwing into bold relief some of the deeper dimensions of questions as diverse as the nature of democracy, the concept of law, and the theory of work. Practical knowledge constitutes a unifying motif of Simon’s entire encyclopedic effort. This volume reconstructs what would have been Simon’s final sustained writing on practical knowledge. It includes reworking of some previously published material, especially the landmark 1961 essay, Introduction to the Study of Practical Wisdom , possibly the best treatment of the concept of command in recent philisophical writing. But it also reproduces, in a form closely corresponding to Simon’s intentions, material drawn from notes and schemata, concerning issues such as the relationship between moral science and wisdom, the nature of practical judgment, and the relationship between practical knowledge and Christian moral philosophy. Also included are previously unpublished letters to Jacques Maritain on the controversy surrounding the theoretical-practical syllogisms, as well as Maritains’s responses. The volume concludes with applications of Simon’s general theory to a critique of the concept of a social science and to the notion of Christian humanism. This volume should appeal to moral philosophers interested in a range of normative issues, as well as social scientists and readers concerned with the philosophical foundations of modern culture. Virtue moralists, in particular, should find in Simon a profound commentator on this tradition in normative ethics.