The supreme advantages of electron microscopy (EM) in the chemical sciences are briefly recalled: By judicious use of electron optical techniques, vital information of a structural, mechanistic, compositional, and often of an electronic kind may be retrieved. Not only are insights gained (through EM) into the existence of whole new families of structures hitherto unperceived, but one also uncovers the structural characteristics of imperfections in solids. And it is often the case that these imperfections reflect or suggest altogether new structures, hitherto unconceived. EM is, therefore, a powerful agent for aiding chemical synthesis of new materials. This is particularly important in the field of heterogeneous catalysis, since altogether new types of catalytic materials may be, on the one hand, defined, described, identified, and characterised, and, on the other, designed and synthesised. There is also the ever-improving role of the electron microscope as an analytical tool: Very few other techniques within reach of the chemist can rival it in its sensitivity and detection limits. (Scanning instruments now permit the imaging and the identification of nanoclusters consisting of just a few atoms.) But there are numerous other branches of chemistry besides catalysis and surface science where EM proves invaluable, as we outline herein, in elucidating structure–property or composition and structure interrelationships.