This working paper provides the formal output from the first workpackage of the TRANSWEL research project (of a total of five workpackages). It presents the main results from 7 months of research work, which ran from February-September 2015. TRANSWEL is a transnational comparative study of regimes of social security portability in the European Union. The transnational element of the study has two aspects: the project investigates portability of social security in 'the European Union' (or 'at EU level'), and between 4 transnational pairs of countries: Austria-Hungary,Germany-Bulgaria, Sweden-Estonia and UK-Poland. It compares social security portability for economically active mobile citizens in four policy areas: unemployment, family benefits, health and pensions.