This volume gives a broad synthesis of the current knowledge and understanding of the plasma physics behind the aurora. The aurora is not only one of the most spectacular natural phenomena on Earth, but the underlying physical processes are expected to be ubiquitous in the plasma universe. Recognizing the enormous progress made over the last decade) through in situ and groundbased measurements as well as theoretical modelling, it seemed timely to write the first comprehensive and integrated book on the subject. Recent advances concern the clarification of the nature of the acceleration process of the electrons that are responsible for the visible aurora, the recognition of the fundamental role of the large-scale current systems in organizing the auroral morphology, and ofthe interplay between particles and electromagnetic fields. Although written by a team of 32 leading scientists from 9 different countries, the book is characterized by consistency in style, nomenclature, notations and format. Extensive cross-referencing helps to integrate the various chapters. The book is intended to be used both as a learning tool for graduate students, and as a reference for space plasma physicists and auroral researchers.