Differential-thermal analysis, X-ray diffraction, and metallography were used to study the interaction between the components of the quasi-ternary CdSe-Ga 2 Se 3-Bi 2 Se 3 system. Phase diagrams of four polythermal sections, the isothermal section at 670 K, as well as a projection of the liquidus surface have been constructed. The projection of the liquidus surface consists of six fields of primary crystallization of the phases, which are separated by 12 monovariant curves and 11 invariant points. The type of mono-and invariant processes in the system has been investigated and the coordinates of the invariant points have been determined. The system is triangulated by the quasi-binary section CdGa 2 Se 4-Bi 2 Se 3 into two subsystems CdSe-CdGa 2 Se 4-Bi 2 Se 3 and CdGa 2 Se 4-Ga 2 Se 3-Bi 2 Se 3. The present results can be employed for the growth of CdGa 2 Se 4 single crystals from non-stoichiometric melts.