This book introduces readers to the basic concepts, classical approaches, and the newest design, development, and applications of biometrics. It also provides a glimpse of future designs and research directions in biometrics. In addition, it discusses some latest concerns and issues in this area. Suitable for a wide range of readers, the book explains professional terms in plain English. Some concepts and designs discussed are so new that commercial systems based on them may not arrive in the market in the next 10 to 20 years.