Authentication is the process of verifying identity, and it forms the first line of defense in access control. In this episode, we explore the different authentication factors: something you know (passwords, PINs), something you have (tokens, smart cards), something you are (biometrics), somewhere you are (location), and something you do (behavioral patterns). We also examine common authentication methods, including single-factor, multi-factor, and risk-based authentication. Understanding how these factors work—individually and in combination—is essential for designing secure systems and passing CISSP exam questions that deal with identity assurance.