This chapter provides a brief introduction to biometrics, what they are and how they are typically used. It discusses different biometric techniques and their particular characteristics and explores some typical applications for the technology within our contemporary world. In addition, it covers some of the rationale behind the wider-scale deployments of biometric technology and places this in a social context, a position which will be reflected in later chapters. The chapter then moves on to discuss why such a book is necessary with respect to the successful and responsible implementation of biometric technology, again placing this within a contemporary context amid other developments. This first chapter consequently sets the tone for the remainder of the book, establishing an important position in relation to the practical, ethical and responsible use of biometric technology.