  We develop a description of the mixed state of type II superconductivity
valid within a wide range of temperatures and external magnetic fields. It is
based on the quasiclassical version of microscopic BCS theory and employs an
expansion in the "distance" from the Hc2(T) line. We prove that in a clean
metal with spherical Fermi surface and isotropic pairing interaction the
superconducting condensation always produces a hexagonal vortex lattice.
