There are many popular assumptions around biometrics and what a biometric identity check really means. Some of these assumptions properly belong in the world of mythology. This chapter clarifies exactly what a biometric identity verification check actually means and how it works technically, covering factors such as matching thresholds and degrees of likeness. Similarly, there exists a degree of misunderstanding around the finer points of individual biometric techniques and their principles of operation. The primary biometric techniques are therefore clarified and placed into perspective. Applications are also discussed with respect to biometric functionality and associated aspirations. This chapter consequently provides an overview of biometric technology, explaining how the technology has evolved, how it works and what it may and may not provide, exploding a few myths along the way. It explores how identity verification has developed as a separate function from early access control systems and looks at some of the currently popular biometric techniques, exploring their strengths and weaknesses accordingly. This chapter provides a solid foundation for those which follow, ensuring that the reader has an adequate working understanding of the technology upon which to develop further thinking.