In 1992 the Maastricht Treaty introduced the formal status of citizenship of the Union, building on previous rights to free movement, residence and non-discrimination for workers, service-providers and service recipients (interpreted to include students since 1985 in Case 293/83 Gravier  ECR 593), and others entitled to free movement under various Directives. The Court of Justice of the European Union in Luxembourg (CJEU), together with national courts, has been a key actor in the development of EU citizenship, with EU legislation reflecting many precepts initially developed by the judiciary (Citizenship Directive 2004).
Citizenship of the Union now extends rights of movement and residence to the non-economically active (retirees for instance), although they usually need to have health insurance and sufficient resources so as not to become an ‘unreasonable burden’ on the host state. The extent to which EU citizens are entitled to equal treatment depends on their economic activity, their degree of integration in the host state and the nature of the benefit claimed. The precise scope of entitlement is subject to intense debate, as explored below.
EU citizenship entails directly effective rights, that is rights which are enforceable in national courts. These rights, in particular residence rights, may only be restricted subject to the principle of proportionality (Case C-413/99 Baumbast  ECR I-7091). Security of residence is an intrinsic feature of EU citizenship, increasing over time. Once the pre-conditions for residence rights are fulfilled, EU law only permits refusal of admittance or deportation of EU citizens representing a ‘genuine, present and sufficiently serious threat affecting one of the fundamental interests of society’. Only individually assessed risks to public policy, public health and public security are permissible grounds, and EU citizens with a permanent right of residence may only be expelled on serious grounds of public policy or public security. (However, some concern has been expressed that some recent EU cases have not properly applied the 2004 Citizenship Directive in this context (Case C-145/09 Tsakouridis  ECR I-11979; Case C-348/09 P.I. Judgment of the Court (Grand Chamber), 22 May 2012 nyr. See also Kochenov and Pirker 2013). The greater the degree of integration within the host Member State ought to lead to greater security of residence (although periods in prison do not count as periods of residence (Case C-400/12 MG and Case C-378/12 Onuekwere. Judgments of the Court, 16 January 2014 nyr).
Current UK practices seem to be in tension with some of these fundamentals. The UK has relied on a lack of self-sufficiency to deport a number of homeless EU citizens, arguing they do not have a right to reside under EU law. While that may be permissible in some cases, each individual case must be scrutinised carefully (Horsley and Reynolds 2014). While residence rights for the non-economically active are conditional on sufficient resources and health insurance, deportation must still comply with the principle of proportionality.