The binary Ca-Li and the ternary Ca-Li-Mg systems were studied experimentally by calorimetry and phase equilibration and also by thermodynamic calculations using the Calphad method. The enthalpy of formation of the binary phase CaLi2 was investigated by drop solution calorimetry in a liquid aluminum bath. Ternary phase equilibria at 150 degreesC were studied with 54 different alloys annealed for 400 h and analyzed by X-ray diffractometry. A thermodynamic assessment of the binary Ca-Li system was performed. All available experimental data agree with the calculation in the binary Ca-Li system. In the ternary Ca-Li-Mg system, a complete ternary solubility of CaMg2 and CaLi2 at 150 degreesC was found. For this Ca(Li,Mg)(2) solution phase, a thermodynamic interaction parameter was assessed. Based on the present thermodynamic datasets and those of the binaries CaMg and Li-Mg from literature, the phase equilibria in the entire ternary system were calculated. Isothermal and vertical sections of the phase diagram and the projection of the liquidus surface are shown. These calculated phase diagrams are well supported by the experimental data.