  We describe the approach of the superconducting state as a sequence of
cross-over phenomena. As the temperature is decreased, uncorrelated pairing of
the electrons leads to the opening of a pseudogap at T_F^*. Upon further
lowering the temperature those electron pairs acquire well behaved itinerant
features at T_B^*, leading to partial Meissner screening and Drude type
behavior of the optical conductivity. Further decrease of the temperature leads
to their condensation and superconductivity at T_c. The analysis is done on the
basis of the Boson-Fermion model in the cross-over regime between 2D and 3D.
