The Middle Ages witnessed a shift in thinking about the way God is related to time. For most of the earlier Middle Ages, scholars had followed an earlier patristic tradition of describing God as eternal and thus as timeless or outside of time. In the early thirteenth century, however, members of the Franciscan order, who played a significant role in the development of the recently-founded universities, re-defined God’s relationship to time in terms of his everlastingness. On their account, God is infinite in temporal duration, rather than simply ’timeless’, since he has no beginning and no end. So construed, God encompasses and is able to relate to every moment in time in a way that the Franciscans believed was not possible on the eternalist account. This book will discuss some of the factors that contributed to their shift in thinking about God as everlasting instead of eternal. Among these, the book will identity a transition in defining the basic nature of God as either simple (for proponents of eternity) or infinite (for proponents of everlastingness) as well as the Franciscan adoption of the metaphysics of the eleventh-century Islamic philosopher, Avicenna.