This paper provides an overview of identity management with emphasis on the federated approaches, covering related standard specifications, and security and privacy considerations. Actual business cases, ranging from B2E to B2C in different industries, such as mobile communications, gaming, and digital TV are introduced. The Liberty Alliance identity frameworks are used as a concrete example to illustrate federated identity management technologies. Moreover, other approaches, such as SAML, shibboleth and WS-Federation, are compared.