In recent years, an important debate has been launched on the possible construction of a fully-fledged European Social Union (ESU), with a view to enhancing the functional coherence and effectiveness of the economic and monetary union as well as its political legitimacy.

The ESU can be understood as the prospective outcome of linking and connecting the five constitutive components of Social Europe, which are:

• The national social space: the ensemble of social protection systems of the 28 member states, resting on the common, typically European tradition of a ‘social market economy’ and “social dialogue”, but characterized by their different endowments of schemes and institutions, different logics and effectiveness in terms of market correcting, different loads of functional and distributive problems, different degrees of “stateness” (administrative performance and capacity to resist social and political captures).

• The EU social citizenship space: the novel membership space – coterminous with the EU external borders – inside which all the bearers of EU citizenship or long-term residence permits enjoy a common ‘title’ bestowed upon them by the Union in order to access the benefits and services of the place in which they freely choose to settle and work, according to the rules of that place. Starting from the 1970s, the EU has put in place an articulated legal framework for the coordination of social security systems of the Member States and since 2011 a directive regulates in its turn the cross-border mobility of patients.

• The transitional social space:the ensemble of social schemes and policies characterized by a cross-border element – a grass root development which took off in the 1990s and has increasingly gained momentum. Most of such initiatives involve regions, under the legal umbrella of European Territorial Cooperation (e.g. euro-regions). Another interesting development on this front is the creation (mainly by the social partners) of cross-border occupational insurance schemes for pensions and health care benefits.

• EU social policy in its ordinary denotation: the ensemble of those supranational policies that have an explicit social purpose, be they of a regulative or (re)distributive nature, directly funded by the EU budget (if they imply spending) and based on either hard or soft law.

• The European social constitution: theset of objectives and principles of a social nature contained in the Treaties, including those that allocate responsibilities between levels of government and define decision-making procedures. Given the supremacy of EU law over national law, such objectives and rules constitute the general framework that guides and constrains the other four components.

According to the theoretical and analytical base of the EuVisions project, ESU should start as a limited, but recognizable system of separate but interdependent elements, subject as in the European Monetary Union (EMU) to common rules and principles and aimed at sustaining/promoting two types of solidarity: a pan-European solidarity between countries and between individual EU citizens centred on supranational institutions, on the one hand, and the more traditional forms of national solidarity, centred on “recalibrated” domestic institutions, on the other one.