  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.
