This chapter introduces Understanding Energy Innovation, a book that is about the process of digital innovation within the electricity sector, with a focus on the social and political. This chapter covers who the book is for, its aims and themes, summarises key theories of energy innovation, and defines smart grids. Smart grids involve the incorporation of new digital and information and communication technologies into utility infrastructures, and they are used as a case study throughout the book to explore energy innovation. The chapter concludes with a brief history of smart grids.