This chapter on creation and eternity in medieval philosophy focuses on arguments for the world's age drawn from the nature of time. To this end, there are four main sections. The first covers proofs for the eternity of the world taken from the nature of time, with an emphasis on Aristotle's original argument for that thesis and then Avicenna's modal version of the proof. The second deals with rejoinders, based upon non‐Aristotelian conceptions of time, to proofs for the eternity of (...) the world with a focus on Augustine's idealist conception of time. The third section takes up positive arguments for the temporal finitude of the cosmos and the difficulties surrounding the idea of infinite past time. The final section canvasses the “agnostic position” of Ibn Tufayl, Moses Maimonides, and Thomas Aquinas concerning the question of the cosmos's age. (shrink)