This chapter discusses the current state of the art of biometric systems. The use of biometrics is an important new part of the design of secure computer systems. However, many users view such systems with deep suspicion and many designers do not carefully consider the characteristics of biometrics in their system designs. This chapter aims to review the current state of the art in biometrics, to conduct detailed study of the available technologies and systems and to examine end-user perceptions of such systems. A framework is discussed that aims to establish guidelines for the design of interactive systems that include biometrics.