The further evolution of the European Union is mainly dependent on how its citizens relate to their fellow Europeans speaking a score of languages and belonging to a variety of cultures. This book addresses the question of whether a new sense of collective self-identification, labeled "European identity," a special form of socio-territorial identities, is emerging. Collective identities are works in progress, they entail a salient strategic-activist and future-oriented-dimension. Divergent strategic goals of the constituent groups induce a perpetual contestation and negotiation of the group identity, a process that in the case of the EU is intensified by the continuously changing boundaries and institutional structure of the super-polity. To confront these challenges, this book has a double focus. The first part weighs in on the feasibility of a European identity in light of what the two main paradigms in the field, primordialism and constructivism, can predict. The second part maps the social forces that are either favorable or inimical to the creation of a common social identity on the continent. Both parts develop hypotheses about the processes we witness, and test them with the available empirical data. Part II distinguishes between passive and active supporters of the integration project, besides the Euroskeptic segment of the public. Provision of public goods by regional integration is believed to explain passive permissiveness, while the main impetus for integration comes from those who may reap above-average benefits from it. This book contends that the groups of active supporters have historically been changing within the Union; namely, the political Left and Right are changing their roles in negotiating future developments. Yet the evolution of the EU is also shaped by the solutions adopted to accommodate ethnic and cultural diversity. The empirical tests involve opinion survey data taken from the Eurobarometer series, World Value and European Social Surveys, and the International Social Survey Programme, expert ratings, as well as party elite documents from the Manifesto Project Database.