This paper aims to find out the factors that affect the formation of European identity, by which the author means a self-identification of individual citizens of the EU member states with this supranational entity. Following a comprehensive and critical review of the main approaches which try to explain the formation of European identity, i.e. the essentialist, rational choice, functionalist, social-psychological, social-constructivist, and neo-institutionalist approaches, the author establishes his hypothesis: what matter most in the shaping of a European identity are the factors of rational choice and institutional construction. This hypothesis is being examined with statistical analyses on the Eurobarometer Trend File Database, as well as against historical experiences.