Energy storage, and in particular electrical storage of energy, has become a very talked about topic in circles ranging from lay persons, in regard to hybrid and battery electric vehicles, to professionals, and certainly by legislators and energy policy makers. This book takes a critical look at the physical storage of electricity in the devices known collectively as electrochemical capacitors and particularly as ultracapacitors. Its 12 chapters cover ultracapacitor and advanced battery topics with an emphasis on a clear understanding of fundamental principles, models and applications. But even to professionals, the distinctions between physical and chemical forms of electric energy storage are unclear and, at times, poorly understood, if at all. The reader will appreciate the case studies from commercial to industrial to automotive applications of not only ultracapacitors, but of these power dense components in combination with energy dense battery technologies.