In the central chapters of this book, Marcin Podbielski and Anna Zhyrkova examine the work of John the Grammarian, Leontius of Byzantium, and Leontius of Jerusalem, showing how, in their writings, a philosophical innovation only associated significantly later with Medieval Latin discourse was brought into existence and clearly formulated: the discovery of the individual, and of the problem of individuation. This discovery, expressed in terms of a radically existential conceptualization of the hypostasis of Christ, as well as of hypostases of created beings, is discussed in counterpoint to the proposals of John Philoponus and Boethius, and also as synthesized, codified and preserved by Maximus the Confessor and John Damascene. Such a diverse group of five early-Byzantine authors, animated by a shared concern to preserve and clarify the Christological doctrine of Chalcedon, resorted to speculative philosophy to create a conceptual vehicle for the Christian doctrine of there being one Christ both truly divine and truly human. Their notion of ?hypostasis? came to designate the subject of natures, existent in its own right and exhibiting all the hallmarks of individuality, found in later Medieval investigations. An inquiry into the philosophical and theological background of this discovery, including a comprehensive historical reconstruction of the concept of hypostasis, makes it possible to show the philosophical and theological novelty of the authors studied, which consists also in their creating a properly Christian approach to philosophical speculation that foreshadows Scholasticism and can be considered a kind of Proto-Scholasticism. The book concludes with an exploration of the philosophical import of the discovery and the model of Christian philosophy it furnishes.