Metaphysics has often held that laws of nature, if legitimate, must be time-independent. Yet mounting evidence from the foundations of science suggests that this constraint may be obsolete. This book provides arguments against this atemporality conjecture, which it locates both in metaphysics and in the philosophy of science, drawing on developments in a range of fields, from the foundations of physics to the philosophy of finance. It then seeks to excavate an alternative philosophical lineage which reconciles time-dependent laws with determinism, converging in the thought of Immanuel Kant.