  The two-dimensional ferromagnetic anisotropic Ashkin-Teller model is
investigated through a real-space renormalization-group approach. The critical
frontier, separating five distinct phases, recover all the known exacts results
for the square lattice. The correlation length $(\nu_T)$ and crossover $(\phi)$
critical exponents are also calculated. With the only exception of the
four-state Potts critical point, the entire phase diagram belongs to the Ising
universality class.
