Microsoft Active Directory Federation Services (AD FS) is a standards-based service that allows the secure sharing of identity information between trusted organisations across a network. When a trust relationship is setup between two organisation’s security realms they are said to have been federated. Users who need to access information from the trusted partner organisations can do so using their normal security credentials. They do not need to have a logon account in the trusted organisation as their authenticated status is passed using AD FS.

ADFS is Microsoft's implementation of the WS-Federation Passive Requestor Profile protocol (passive indicates that the client requirements are just a cookie- and JavaScript-enabled Web browser). AD FS implements the standards based WS-Federation protocol and Security Assertion Markup Language (SAML).