  In this thesis work we have employed two microscopic models (ladder-QCD and
Nambu-Jona-Lasinio) for describing the properties of the QCD phase diagram at
finite temperature and quark densities. In particular, we have studied the
mechanism of meson condensation at finite isospin and strangeness chemical
potentials, and its competition with ``standard'' scalar fermionic condensates.
In the last chapter, a detailed study of the chiral critical line at finite
chemical potentials has been performed, achieving a remarkable agreement with
recent lattice data.
