William of Ockham (c. 1287-1347) is known to be one of the major figures of the late Middle Ages. The scope and significance of his doctrine of human thought, however, has been a controversial issue among scholars in the last decade, and this book presents a full discussion of recent developments. Claude Panaccio proposes a richly documented and entirely original reinterpretation of Ockham's theory of concepts as a coherent blend of representationalism, conceptual atomism, and non reductionist nominalism, stressing in the process its special interest for current discussions in philosophy of mind and cognitive sciences.