The concept of ion-exchange transformation in heterogeneous thin film–aqueous solutions of metal substituents is presented as a promising way of synthesizing multicomponent compounds based on metal chalcogenides. Characteristic features of this process are described and a number of its physicochemical patterns are revealed using data obtained at Yeltsin Ural Federal University’s Faculty of Physical and Colloid Chemistry with thin-film solid solutions of SnxPb1–xSe, CdxPb1–xS, AgxPb1–xS, HgxPb1–xSe, SnxPb1–xS of different compositions. The organization of ion-exchange synthesis is considered, starting from preliminary calculations and ending with interpretation of the final results. The effect the temperature, the morphology and crystal structure of the initial film, the composition of aqueous solution, and the metal substituent have on the depth of the process is described. Data on the solid-phase diffusion of lead ions in a CdS film are presented.