As the capabilities of mobile devices increase, their security is becoming more of an issue. Passwords and PINs are the lowest forms of security, yet they are the most widely used. Continuous authentication using behavioral biometrics and multimodal biometrics provides a way to greatly increase security. Using behavioral biometrics, such as linguistic profiling, keystroke dynamics, and behavior profiling, with text messages is a good way to analyze data and determine the identity of the user. Deciding which forms of authentication to use depends on the system the security is being provided for. User authentication in the workplace is a major concern. An effortless way to improve security would be to use a biometric-enabled bracelet to authorize and de-authorize a user when using a computer and when walking away. This book extensively surveyed the biometric user-authentication and particularly focused on mobile biometric authentication including emerging biometric authentication processes.