Selected recent works from the authors' laboratory on the intrinsic electronic and structural properties of early transition metal oxide clusters are reviewed. These clusters provide well-defined molecular models pertinent to mechanistic understandings of complex oxide surface chemistry and catalysis. The energy gap evolution with cluster size was probed for the stoichiometric (TiO2)(n) , (V2O5)(n) , and (CrO3)(n) clusters, and each system was shown to approach the band gap of bulk oxides in a unique way. A variety of other model clusters have been characterized, such as the oxygen radical or diradical on a single W6+ site in WO4 /WO4, the superoxide (WO3)(n)(O-2 ) complexes for dioxygen activation, and terminal versus bridging oxygen in M3O2 (M = Nb, Ta) clusters. Novel chemical bonding has been observed in a number of oxide clusters. The W3O9 and W3O92 clusters were found to possess d-orbital aromaticity, whereas delta-aromaticity was discovered in the Ta3O3 cluster. (C) 2010 Elsevier B. V. All rights reserved.