  The Thermal Renormalization Group can be employed to study the dynamics of
$T\neq 0$ Quantum Field Theories close to second order phase transitions, where
neither resummed perturbation theory nor first principle lattice simulations
can be employed. As an example, I discuss the computation of the plasmon
damping rate in the scalar field theory from $T\gg T_C$ down to $T_C$. As the
critical point is approached, the lifetime of long wavelength thermal
fluctuations diverges. Taking this effect into account, the notion of
quasiparticle, and kinetic approaches, can be extended close to the critical
regime. The consequences on the scenarios for topological defect formation in
the early universe are also discussed.
