Sulfide-induced intergranular corrosion (IGC) of copper was documented in salt water under free corrosion or controlled potential. The process was promoted by the oxidizing potential and the sulfide ions. A transition potential, E-t, of about -0.15 V (Ag/AgCl) was identified in the polarization curves in the presence of sulfide ions. Above E-t, sulfide ions accelerate IGC while having a modest effect on the rate of copper dissolution. Below E-t, they promote copper dissolution, while IGC occurs much more slowly. Various sulfur species were detected in the corrosion product using X-ray photoelectron spectroscopy.