Rae Langton offers a new interpretation and defence of Kant's doctrine of things in themselves. Kant distinguishes things in themselves from phenomena, and in so doing he makes a metaphysical distinction between intrinsic and relational properties of substances. Kant says that phenomena--things as we know them--consist 'entirely of relations'. His claim that we have no knowledge of things in themselves is not idealism, but epistemic humility: we have no knowledge of the intrinsic properties of substances. This humility has its roots in some plausible philosophical beliefs: an empiricist belief in the receptivity of human knowledge and a metaphysical belief in the irreducibility of relational properties. Langton's interpretation vindicates Kant's scientific realism, and shows his primary/secondary quality distinction to be superior even to modern-day competitors. And it answers the famous charge that Kant's tale of things in themselves is one that makes itself untellable.