Recently, we studied the interaction of supported metal nanocluster catalysts with reactive gases at elevated temperatures by means of in situ high resolution transmission electron microscopy (HRTEM). This paper will briefly review this work to illustrate the in situ HRTEM capability for studies of the surface structures and the dynamics of supported metal nanoclusters. at the atomic scale and to discuss the possibilities of including such insight into the description of their catalytic properties. (c) 2005 Elsevier B.V. All rights reserved.