An analysis of the structural properties of vapor-liquid equilibrium (VLE) diagrams provides a fundamental understanding of the thermodynamic behavior of azeotropic mixtures upon distillation.In addition to a review of well-known fundamental work on the analysis of VLE diagrams, this survey comprises less-known published results, especially from the Russian literature. Some new results are also presented for the first time. (C) 2003 Elsevier Science Ltd. All rights reserved.