Phase equilibria in the AgI-Ag7GeSe5I-GeSe2 system were studied by differential thermal and X-ray diffraction analysis. T-x phase diagrams of boundary systems, liquidus surface projection and a number of internal vertical sections of the T-x-y diagram were constructed. It was found that all three boundary systems are quasi-binary and form eutectic phase diagrams. The AgI-Ag7GeSe5I-GeSe2 system is a quasi-ternary plane of the corresponding quaternary system and belongs to the type with invariant eutectic crystallizing at 525 0C. The liquidus surface projection consists of 3 regions corresponding to the primary crystallization of the α-phase based on Ag7GeSe5I, as well as high-temperature modifications of the AgI and GeSe2 compounds. The liquidus surfaces of HT-GeSe2 and the α-phase, which have a higher melting point, occupy very large areas, while the liquidus surface of the HT-AgI phase is located in a small region near the corresponding vertex of the concentration triangle.