  We study, both numerically and analytically, the development of equilibrium
after preheating. We show that the process is characterised by the appearance
of Kolmogorov spectra and the evolution towards thermal equilibrium follows
self-similar dynamics. Simplified kinetic theory gives values for all
characteristic exponents which are close to what is observed in lattice
simulations. The resulting time for thermalization is long, and temperature at
thermalization is low, $T \sim 100$ eV in the simple $\lambda \Phi^4$
inflationary model. Our results allow a straightforward generalization to
realistic models.
