The Al2O3-CaO-SiO2 system provides the basis for describing many important chemical processes. Although the system has previously been extensively studied, recent advances in experimental technique have provided the opportunity to obtain accurate liquidus measurements in the low-silica region at fixed temperatures. The experimental procedures involve equilibration of high-purity oxide powder mixtures at selected temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X-ray microanalysis. The liquidus isotherms have been determined at selected temperatures between 1503 and 1873 K in the anorthite, gehlenite, pseudowollastonite, corundum, CaAl12O19, CaAl2O6, lime, Ca3SiO3, and Ca2SiO4 primary phase fields. The results are compared with currently available thermodynamic model predictions of the phase chemistry.