Citizens' Rights Directive

The Citizens' Rights Directive 2004/38/EC (also sometimes called the "Free Movement Directive") sets out the conditions for the exercise of the right of free movement for citizens of countries in the European Economic Area (EEA), which includes the member states of the European Union (EU) and the three European Free Trade Association (EFTA) members Iceland, Norway and Liechtenstein. Switzerland, which is a member of EFTA but not of the EEA, is not bound by the Directive but rather has a separate multilateral sectoral agreement on free movement with the EU and its member states.

Source: Wikipedia — Citizens' Rights Directive (CC BY-SA 4.0)