Biometric Authentication is a type of User Authentication with factors in the Inherence category: "Something the user is". Out of the three authentication factor categories, it is considered to be the most difficult to forge. It is also a major area of current research.
High-security environments have been using biometric authentication for many years. Apple's recent addition of TouchID fingerprint recognition on the iPhone has taken biometrics mainstream. Now millions of users have a biometric authentication device right in their pocket. It has been reported that Apple is planning to add TouchID to laptops soon. Third-parties can use the iPhone's TouchID as user authentication. For example, Amazon.com's iPhone application uses it to authorize purchases.
The most commonly used and researched biometric factors used for authentication are: