The results of a complex investigation on the phase equilibria and thermodynamic properties of the system Tl–In–Te, obtained using differential thermal analysis, X-ray phase analysis, and electro motive force (EMF) measurement are presented. A projection of the liquidus surface, an isothermal section at 300 K, and a series of vertical sections [Tl(Tl 2 Te)–InTe, TlInTe 2 –Tl(In, Te, Tl 5 Te 3 )] of the phase diagram are obtained. The types and coordinates of the nonvariant equilibria are determined. It was established that in this system two intermediate phases of variable composition (c and e) based on the ternary compounds TlInTe 2 and Tl 3 InTe 2 are formed. Wide regions of homogeneity based on the binary compounds Tl 2 Te, Tl 5 Te 3 , TlTe, InTe, and In 2 Te 3 were also detected. Based on the results obtained by EMF measurements, using concentration galvanic cells, the relative partial molar values for thallium and the standard integral thermodynamic functions of the formation for the ternary compounds and solid solutions were derived.