  We report here recent analytical and numerical work on the theoretical
treatment of the early stages of heavy ion collisions, that amounts to solving
the classical Yang-Mills equations with fluctuating initial conditions. Our
numerical simulations suggest a fast isotropization of the pressure tensor of
the system. This trend appears already for small values of the coupling
constant $\alpha_s$ . In addition, the system exhibits an anomalously small
shear viscosity.
