The behaviour of inclusions on the surface of molten steel and at molten steel-slag interfaces was observed in-situ using a Confocal Scanning Laser Microscope (CSLM). Solid irregular and liquid spherical inclusions were observed on the molten steel surfaces. They were found to cluster and agglomerate, driven by capillary depression forces and they were identified as Al2O3-MnO-SiO2, Al2O3-MnO and Al2O3 particles in quenched samples. At steel-slag interfaces, inclusion clustering was also observed. Here a weak repulsive force was found to oppose fluid flow driven clustering. The inclusions were found to react with the slag and to undergo changes in shape, size and chemistry. Examination of the interface after the experiments revealed that the inclusions were enriched in CaO, SiO2 and Al2O3 from the slag.