  With the exception of confinement the three-dimensional Nambu-Jona-Lasinio
(NJL_3) model incorporates many of the essential properties of QCD. We discuss
the critical properties of the model at nonzero temperature T and/or nonzero
chemical potential $\mu$. We show that the universality class of the thermal
transition is that of the d=2 classical spin model with the same symmetry. We
provide evidence for the existence of a tricritical point in the
($\mu$,temperature) plane. We also discuss numerical results by Hands et al.
which showed that the system is critical for $\mu>\mu_c$ and the diquark
condensate is zero.
