Electron microscopy is undoubtedly one of the most important tools for visualizing the morphology of industrial heterogeneous catalysts. With improvements in resolution, it is now possible to directly image the complex nanostructure of catalytic materials. Spectroscopic measurements performed in situ within the microscope provide elemental analysis and information on oxidation state and bonding. The development of in situ, controlled atmosphere instruments means that we can now study working catalysts, instead of simply doing postmortem examinations. In this review, we assess the state of the art and highlight some of the insights provided by microscopy in the study of catalysts. We then look to the future to see the developments on the horizon (notably aberration-corrected microscopy) that could have the largest impact on our ability to understand catalysts. (C) 2003 Elsevier Science (USA). All rights reserved.