  The cluster variation method (CVM) is an approximation technique which
generalizes the mean field approximation and has been widely applied in the
last decades, mainly for finding accurate phase diagrams of Ising-like lattice
models. Here we discuss in which cases the CVM can yield exact results,
considering: (i) one-dimensional systems and strips (in which case the method
reduces to the transfer matrix method), (ii) tree-like lattices and (iii) the
so-called disorder points of euclidean lattice models with competitive
interactions in more than one dimension.
