  In this paper we consider the problem of finding periodic solutions of
certain Euler-Lagrange equations, which include, among others, equations
involving the $p$-Laplace and, more generality, the $(p,q)$-Laplace operator.
We employ the direct method of the calculus of variations in the framework of
anisotropic Orlicz-Sobolev spaces. These spaces appear to be useful in
formulating a unified theory of existence for the type of problem considered.
