By means of an optimization procedure, the ternary Ag–Au–Pb system has been assessed. All available experimental data of the ternary system and the results derived from thermodynamic descriptions for the three limiting binary systems are used. For the Ag–Au and Au–Pb systems, optimized Gibbs energy expressions were taken from the literature. A new assessment of the binary Ag–Pb system based on our calorimetric investigations is presented in this paper. Calculated phase diagrams and some calculated thermochemical functions for the binary Ag–Pb and the ternary Ag–Au–Pb systems are compared with experimental data.