In this paper, we focus on the concept of size of country (or economy). Specifically, within the European Union (EU), we look for growth discrepancies between countries according to their size. We try to explain growth differential using arguments related to the size of countries. Thus, we highlight that the European construction, in particular, the Economic and Monetary Union (EMU) is an asymmetric process favoring both small countries and the development of non-cooperative growth policies. Among them, we are particularly interested in the introduction of tax competition as a growth policy in some countries. This policy should be seen as an opportunist strategy of small countries harmful for the overall growth of the EU.