The entire phase diagram of the Cu-In system was investigated using differential scanning calorimetry (DSC), powder X-ray diffraction (XRD). metallography and electron probe microanalysis (EPMA) studies. The results indicate the existence of a solubility region of In in Cu with the limit of the solid solution at 5.20 at.% In at 400 degreesC and of six intermediate phases, the three low-temperature phases delta, eta and Cu11In9, and the three high-temperature phases gamma, eta' and beta. The boundaries of each phase were defined with respect to temperature and composition.