The need to control or eliminate sulfur dioxide emissions from sulfide smelters has increased the drive to develop new processes for the extraction of metal from sulfide minerals. One such process currently gaining interest is the lime-enhanced reduction of metal sulfides. This paper discusses the thermodynamic aspects relevant to chalcopyrite, chalcocite, and pyrrhotite reduction with hydrogen, carbon monoxide, or carbon in the presence of lime. The effects of temperature and gas composition on sulfide reduction are also discussed. ΔG°vs T diagrams for lime-enhanced sulfide reductions with hydrogen, carbon monoxide, and carbon are constructed and discussed together with some experimental results produced by the authors.