An identity federation (or just federation) is a collection of organizations that agree to interoperate under a certain rule set. This rule set typically consists of legal frameworks, policies and technical profiles and standards. It provides the necessary trust and security to exchange identity information to access services within the federation.
Some federations also distinguish the organisations that participate. Often there are federation members (e.g. universities and research institutes), which operate services and provide identities, and federation partners (e.g. commercial companies that offer services to higher education users), which only operate services.
In the context of SAML-based federations, there are the following technical components:
As of 2017, most western countries operate one or more identity federations for their higher education and research community. Most academic identity federations are operated within the borders of one single country. Their members are mostly education (e.g. universities) and research organisations (research facilities) within that country, as well as the services they operate. Most of them were established by the local national research and education network. Such federations are also called national federations. The first national federations were established around 2005.
A list of current national federations can be found on the REFEDS web page and in greater detail on the REFEDS federations web page.
There are also federations, which are not operated for members within a single national country but for members of a particular community. One of the first such examples is the CLARIN Service Provider federation, which is operated by the language researchers of the international CLARIN research project.
There are also interfederation services whose scope go beyond that of a single country. Notably, the Kalmar Union (decomissioned in April 2017) and eduGAIN. They are however not typicial federations but rather interfederation services, which means that they help interconnecting existing national federations instead of fully incorporating all their entities in a superset, a confederation.
To get an up-to-date answer for this question, please refer to the REFEDS federations page. REFEDS is a group of Research and Education FEDerations funded mostly by a few National Research and Education Networks and the Internet Society.
eduGAIN is a service that interconnects the participating identity federations. They agree on a set of common standards and policies which ensure interoperability. eduGAIN is therefore also called an interfederation service. Its goal is to enable Pan-European Web Single Sign On (Web SSO) for members of the research and education community.
The eduGAIN interfederation service is intended to enable the trustworthy exchange of information related to identity, authentication and authorisation between the member federations. The eduGAIN service delivers this through co-ordinating elements of the federations' technical infrastructure and a policy framework controlling the exchange of this information.
More overview information can be found on www.edugain.org.