  The extrapolation of truncated perturbative series to the large coupling
regime is not reliable since the accuracy of the calculations cannot be
improved systematically by a finite set of higher order terms. Instead, a
nonperturbative approach is proposed here to describe the thermodynamics of
strongly coupled plasmas. Within the $\phi^4$ theory, it is derived from the
Luttinger-Ward theorem and amounts to a quasiparticle description. The approach
is extended to the quark-gluon plasma. Even close to the confinement
temperature it is found to be in a good agreement with lattice data of several
gauge systems. The model is applied to predict the equation of state of the
quark-gluon plasma with realistic quark masses.

High Energy Physics - Phenomenology