This book is an introduction to electron holography, a newly developed technique for observing and measuring microscopic structures of matter and fields using the wave nature of electrons. It describes principles, experimental details, and observation examples for vortices in superconductors, the magnetic domain structure in ferromagnets, and for fundamental phenomena of quantum mechanics such as the single-electron build up of an interference pattern and the Aharonov-Bohm effect. The most recent information in this rapidly evolving field is included in this new edition, for example, the dynamical observation of vortices in superconductors.