Electron Microscopy in Heterogeneous Catalysis describes the unique role electron microscopy plays in the immensely important field of heterogeneous catalysis. It brings together several disciplines, namely surface science, solid state chemistry and physics, materials science, chemical engineering and crystallography. The work described in this monograph exemplifies the many striking advances made by electron microscopy in advancing our understanding and creating advanced catalyst materials and processes. Catalysis plays a pivotal role in national economies and controls more than 90% of the world’s chemical manufacturing processes. In many technological processes, catalysts are increasingly nanoscale heterogeneous materials. With growing regulatory guidelines requiring efficient and environmentally compatible catalytic processes for selective hydrocarbon catalysation and for creating new energy sources, it is crucial to have a fundamental understanding of the nanostructure of the catalyst and the mechanisms involved to design novel catalysts and processes. As we show in the following chapters, electron microscopy is playing a direct role in the development of catalytic materials and reactions. Pioneering developments in atomic-resolution environmental transmission electron microscopy (ETEM) for directly probing the catalyst’s behaviour during the reaction at the atomic level, wet ETEM for studying catalyst-liquid reactions dynamically at the molecular level, field-emission low-voltage high-resolution scanning electron microscopy (LVHRSEM), atomic-resolution scanning TEM and electron-induced analytical spectroscopic (AES) methods address the fundamental issues of the materials and processes in catalysis. All these techniques are playing a unique role in obtaining insights into active sites, the atomic structure, atomic scale chemistry, point and extended defects and surface reconstruction, the nature of bonding and the electronic structure of the surface and the related subsurface of the catalyst and the mode of operation. These modifications govern the relationships between structure and activity in catalytic reactions and identify the factors that control the activity, selectivity and the activation barrier. New opportunities have evolved in catalysis research as a direct consequence of electron microscopy.