The ongoing processes of internationalization and globalization have led to a genuinely borderless world economy with a strong regional focus. This paper examines the European Union and to what extent this region is economically integrated over the years spanning from 1982-2006, by mapping the nature and development of Foreign Direct Investments within the EU15. In order to study the degree of European economic integration, the structural, institutional and functional mode of integration is analyzed. The empirical results show that the economic structures of EU countries converged over time and that the institutional environment breeds a positive impact on the European integration process. Furthermore, the longitudinal study of intra- regional FDI data is appropriate to analyze the evolving FDI network relations in a temporal dimension. This paper indicates that the dominancy of central European countries slightly decreases, while the periphery region emerges within the EU. In addition, the nature of the intra-European production network has developed into a highly complex network with increasing interdependency among all EU countries.