The system silver–indium–gallium has been investigated by the standard techniques of thermal analysis, photomicrography, X-ray photography, and hardness testing. The smallness of the heat effects made the determination of the liquid surface indefinite, at least in the low-temperature region where the pronounced tendency for metastable liquid phase to persist rendered all measurements indefinite, but the room-temperature isotherm was determined with more certainty. Owing to the complexity of the diagram there is still some uncertainty about some areas.A one-phase area (α phase) exists in the silver-rich region of the ternary isotherm, representing the solid solubility of indium and gallium in silver. The silver-rich intermediate phase in the system silver–indium, δ, is shown to have a close-packed hexagonal structure and its lattice constants have been determined. The structure of γ, the corresponding phase in the system silver–gallium is more complex and was not determined. δ and γ phases do not form a continuous one-phase region.Ternary peritectics exist at 623 °C and 600 °C (approximately). It is possible that two peritectics exist at the latter temperature, in close proximity.The ternary eutectic lies at 14.5 °C and has an approximate composition of 2% silver, 24% indium, and 74% gallium.