One of the most debated topics in medieval philosophy was the metaphysics of identity—that is, what accounts for the distinctness (non-identity) of different individuals of the same, specific kind and the persistence (self-identity) of the same individuals over time and in different possible situations, especially with regard to individuals of our specific kind, namely, human persons. The first three papers of this volume investigate the comparative development of positions. One problem, considered by William of Auvergne and Albert the Great, deals with Aristotle's doctrine of the active intellect and its relation to Christian philosophical conceptions of personhood. A larger set of issues on the nature and post-mortem fate of human beings is highlighted as common inquiry among Muslim philosophers and Thomas Aquinas, as well as Aquinas and the modern thinker John Locke. Finally, the last two papers offer a debate over Aquinas's exact views regarding whether substances persist identically across metaphysical "gaps" (periods of non-existence), either by nature or divine power.