This article gives an overview of preparation, characterization, and activity/selectivity of bulk and dispersed metal sulfide catalysts prepared from two families of molecular complexes. New promoter metals are identified. Behavioral features of these molecular-complex-derived catalysts for different hydroprocessing applications are discussed. These catalysts share some common characteristics that make them distinct from conventional Al2O3-supported catalysts. Examples are given to show the importance of understanding catalyst-feedstock interactions and balancing catalyst hydrogenation and hydrogenolysis functionalities. (c) 2007 Elsevier B.V. All rights reserved.