A parametric crossover equation of state for pure fluids which incorporates the scaling laws asymptotically close to the critical point and is transformed into the regular classical expansion far away from the critical point is adapted to binary mixtures. An isomorphic generalization of the law of corresponding states is applied to the prediction of the thermodynamic properties and the phase behavior of binary mixtures over a wide region around the locus of vapor-liquid critical points. Methane-ethane and methane-propane are used as reference mixtures, and model parameters for other mixtures are determined completely from excess critical compressibility factors. A comparison is made with the experimental data for twelve binary mixtures. The crossover equation yields a satisfactory representation of the thermodynamic property data in a large range of temperatures and densities. Results for the ammonia-water mixture are consistent with an independent classical correlation.