A theoretical formalism to calculate the phase diagrams of polymer/liquid crystal mixtures is presented. Mixtures involving linear and crosslink-ed polymers together with low molecular weight nematic and smectic-A liquid crystals are considered. The generalization to binary mixtures of nematogens is briefly shown. The method of calculating model phase diagrams of side chain liquid crystal linear and crosslinked polymers in either isotropic or nematic solvents is presented. In nematogen mixtures, the coupling parameter induces tremendous changes in the miscibility of both linear and crosslinked polymers with low molecular weight analogous or different liquid crystals. Applications of the theoretical formalism are given.