Metal smelting is seeing a continual increase in intensity and throughput in recent years. This is done with increasing demand for cost/capital efficiency, higher recovery, and managed environmental impact, among other things. With the development of more intense smelting processes, the issues of refractory wear, mixing and separation of reacting phases and the nature of the reactions between them become more prominent. Understanding of interfacial phenomena is in growing need, in addition to knowledge of the bulk properties of equilibrium and transportation. The GKW CRC has a suite of projects aimed at developing various techniques and expertise to provide information of interfaces in metallurgical systems. This article illustrates some recent development in this area, particularly in studies of melt/refractory contacts, the determination of surface and interfacial tension of metal/slag/matte melts, modelling slag-metal mixing and studies of kinetics of the smelting reactions.