The Fe – Ni – S, Cu – Ni – S and Cu – Fe – S systems form the basis of matte melts, which are the product of processing copper-nickel and copper sulphide concentrates, as well as oxidized nickel ores. Processing of the latter involves sul-phidizing. Information about the phase diagrams of the Fe – Ni – S, Cu – Fe – S and Cu – Ni – S systems and their thermodynamic properties is necessary to describe py-rometallurgical processes involving Cu, Ni and Fe in order to understand how the metals distribute between the matte and the slag. If one knows the properties of sulphur dissolved in the considered melts, one can analyze its behaviour during sulphide concentrate melting and matte conversion. This paper aims to look at the thermodynamic properties of sulphide systems containing iron, nickel and copper.