This document introduces FIDO, a passwordless authentication standard that provides more secure login than legacy multi-factor authentication and PKI methods. It works by registering devices, then allowing login through those registered devices without the need for passwords, SMS codes, or other single-use tokens. FIDO authentication is standardized across major vendors, decentralized by using local devices for authentication rather than centralized assets, and resistant to phishing since it doesn't rely on shared secrets, biometrics, or passwords.