  I review dynamical chiral symmetry breaking in four-fermi models, including
results of Monte Carlo simulations with dynamical fermions. For 2<d<4, where
the phase transition defines an ultraviolet fixed point of the renormalisation
group, the continuum theory may either be describable using the large-N_f
expansion, as in the case of the Gross-Neveu model, or be intrinsically
non-perturbative, as in the case of the Thirring model. For d=4, the models are
trivial and are described by a mean field equation of state with logarithmic
corrections to scaling, which may nonetheless define new universality classes
distinct from those of ferromagnetism.
