📓 The state of the art in detection and quantitative determination of phase composition, surface composition and various compositional inhomogeneities in the chemical composition of heterogeneous catalysts is discussed. The principles of stoichiography and stoichiographic methods, which have recently been introduced into analytical chemistry, as well as main theoretical and practical notions of the advanced stoichiographic method of differential dissolution (DD) are reported. The unique feature of the DD method, distinguishing it from all other methods for determination of the composition and structure of multielement multiphase solid substances, is that reference samples of solid phases are not necessary for the analysis. This feature of the DD method allows simultaneous detection, identification and quantitative determination of various manifestations of spatial inhomogeneity in the chemical composition of inorganic solids. Publications devoted to application of the DD method for determining the chemical composition of various heterogeneous catalysts are reviewed.