  We investigate the phase diagram of strongly interacting matter as a function
of temperature and baryonic density/chemical potential, within
Nambu--Jona-Lasinio type models. We perform a systematic study concerning the
existence, location, and properties of a critical end point/tricritical point,
both in SU(2) and SU(3) versions of the model. We verify that, for $m_u=m_d=0$
and up to a critical strange quark mass, there is a tricritical point, which
becomes a critical end point in a world with realistic values of the current
quark masses. The properties of physical observables, such as the baryon number
susceptibility and the specific heat, are analyzed in the vicinity of the
critical end point, with special focus on their critical exponents. The
behavior of mesons in the $T-\mu_B(\rho_B)$ plane is analyzed in connection
with possible signatures of partial and effective restoration of chiral
symmetry.
