The ternary alloy system Ag-Cu-Si was investigated in detail for the first time. The phase diagram was analysed by means of light optical microscopy, powder x-ray diffraction, differential thermal analysis (DTA) and scanning electron microscopy in combination with energy dispersive x-ray spectroscopy. The complete isothermal section at 650 °C was studied experimentally, and several additional samples were studied in order to obtain insight into phase equilibria with the high-temperature phases of the binary Cu-Si system. DTA studies in two vertical sections were used to determine ternary invariant phase reactions and to construct the ternary reaction scheme (Scheil diagram). A liquidus surface projection was constructed by combining these data with microstructure analysis of selected as-cast samples.