Biometrics is a rapidly evolving field with applications ranging from accessing one's computer to gaining entry into a country. The deployment of large-scale biometric systems in both commercial (e.g., grocery stores, Disney World, airports) and government (e.g., IAFIS) applications has served to increase the public's awareness of this technology. This rapid growth has clearly highlighted the challenges associated with designing and deploying biometric systems. Indeed, the problem of biometric authentication is a "Grand Challenge" in its own right. The past five years has seen a significant growth in biometric research resulting in the development of innovative sensors, new algorithms, enhanced test methodologies and novel applications. The purpose of the Handbook of Biometrics is to address this void by inviting some of the prominent researchers in Biometrics to author individual chapters describing the fundamentals as well as the latest innovations in their respective areas of expertise. Designed for researchers and advanced-level students in computer science, the Handbook of Biometrics is also suitable for Biometric and Computer Security professionals.