We give the first rigorous derivation of the celebrated
Ginzburg-Landau (GL) theory, starting from the microscopic Bardeen-
Cooper-Schrieffer (BCS) model. Close to the critical temperature, GL
arises as an effective theory on the macroscopic scale. The relevant
scaling limit is semiclassical in nature, and semiclassical analysis,
with minimal regularity assumptions, plays an important part in our proof.