The eXtensible Access Control Markup Language (XACML) OASIS Standard is an XML-based language for access control.

XACML describes both an access control policy language and a request/response language. The policy language is used to express access control policies ('who can do what when'). The request/response language expresses queries about whether a particular access should be allowed (requests) and describes answers to those queries (responses).

XACML and SAML 

The newest versions of XACML and SAML have been designed to complement each other; for example, an XACML policy can specify what a provider should do when it receives a SAML assertion, and XACML-based attributes can be expressed in SAML.