This document provides an outline and overview of biometrics and biometric systems. It begins with definitions of biometrics and describes the main components of a biometric system, including the sensor, feature extraction, matching, and database modules. It then covers various biometric techniques including fingerprint, iris, retina, face, voice, signature, and hand scans. It discusses identification vs verification modes and types of errors in biometric systems. Application areas are identified as well as limitations of unimodal systems. Finally, it introduces multimodal biometric systems and different levels of fusion.