"Welfare tourism" expresses the concern that individuals use the right of free movement of persons with a view to benefiting from a more favourable welfare system. The principle of free movement of persons entitles EU citizens to reside in another Member State, under certain conditions. Only limited restrictions can curtail this right, namely temporary restrictions based on the Accession Treaties, agreed for the recent enlargements. Even if there are very few barriers to free movement, intra-EU mobility is limited and most of it is directed to EU 15. National social security systems are coordinated to ensure that free movement of persons is not hindered. Expenditure on social protection is spread across a range of welfare benefits in broadly similarly shares throughout the EU. Assessing the impact of immigration is not straightforward. Some elements can help to assess its impact on social security, but those studies which do exist stress the lack of data relevant to the issue, and the limited impact on welfare systems. Current concerns about "welfare tourism" mobility relate in particular to the imminent ending of transitional arrangements.