This book focuses on the use of novel electron microscopy techniques to further our understanding of the physics behind electron-light interactions. It introduces and discusses the methodologies for advancing the field of electron microscopy towards a better control of electron dynamics with significantly improved temporal resolutions, and explores the burgeoning field of nanooptics - the physics of light-matter interaction at the nanoscale - whose practical applications transcend numerous fields such as energy conversion, control of chemical reactions, optically induced phase transitions, quantum cryptography, and data processing. In addition to describing analytical and numerical techniques for exploring the theoretical basis of electron-light interactions, the book showcases a number of relevant case studies, such as optical modes in gold tapers probed by electron beams and investigations of optical excitations in the topological insulator Bi2Se3. The experiments featured provide an impetus to develop more relevant theoretical models, benchmark current approximations, and even more characterization tools based on coherent electron-light interactions.