The catalytic performance of MoS2-based hydrotreating catalysts strongly depends on their morphology and orientation on the support. The effects of the morphology and orientation of MoS2 clusters on supports, typically Al2O3 and TiO2, on the catalytic performance are reviewed here, focusing on recently reported epitaxial relationships at the interface between MoS2 clusters and the support. (C) 2003 Elsevier B.V. All rights reserved.