This volume contains fourteen contributions to the topic of weakness of will in medieval philosophy. It fills an important gap in current research by presenting Aristotelian and non-Aristotelian medieval accounts of "akrasia", many of which have not yet been the object of scholarly writing. They are not only of great intrinsic philosophical interest; they also eminently document the transformation of ethical thought in the Middle Ages. Weakness of will is a test case for a wider range of problems in moral psychology and ethical theory. The articles collected in this volume give insight into a variety of accounts of practical rationality that were directly or indirectly influential on modern thinkers. The temporal framework of the volume exceeds the Middle Ages on both ends by including Aristotle and authors from the Renaissance and the Reformation.