A complete critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties of the MgO-Al2O3-CrO-Cr2O3 system at 1 bar total pressure are presented. Optimized equations for the thermodynamic properties of all phases are obtained which reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25 degrees C to above the liquidus temperatures at all compositions and oxygen partial pressures. The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram section.