Critical Behavior of $\phi^{4}$-Theory from the Thermal Renormalization Group

We discuss the universal critical behavior of a selfinteracting scalar field theory at finite temperature as obtained from approximate solutions to nonperturbative renormalization group (RG) equations. We employ a formulation of the RG-equations in real-time formalism which is particularly well suited for a discussion of the thermal behavior of theories which are weakly coupled at T=0. We obtain the equation of state and critical exponents of the theory with a few percent accuracy even for a relatively simple approximation to the exact renormalization group equations