In the Critique of Pure Reason, Kant famously criticizes traditional metaphysics and its proofs of immortality, free will and God's existence. What is often overlooked is that Kant also explains why rational beings must ask metaphysical questions about 'unconditioned' objects such as souls, uncaused causes or God, and why answers to these questions will appear rationally compelling to them. In this book, Marcus Willaschek reconstructs and defends Kant's account of the rational sources of metaphysics. After carefully explaining Kant's conceptions of reason and metaphysics, he offers detailed interpretations of the relevant passages from the Critique of Pure Reason (in particular, the 'Transcendental Dialectic') in which Kant explains why reason seeks 'the unconditioned'. Willaschek offers a novel interpretation of the Transcendental Dialectic, pointing up its 'positive' side, while at the same time it uncovers a highly original account of metaphysical thinking that will be relevant to contemporary philosophical debates.