This briefing discusses the challenges of the European Union enlargement. In turn, this increase in membership caused challenges. The EU is not only larger; it is more cumbersome, more diverse and more expensive. How the EU adapts to these challenges will determine not just the internal dynamics of the ’union’, but its external presence as well. Hence it is time for Europe’s major partners in the world to take the implications of a changed EU into account. The problem of decision-making is three fold. To begin with, larger groups have more difficulty making decisions than smaller groups. No matter what the number of countries involved, the institutions of European Union is unwieldy and decision-making authority is poorly distributed. The informal practice of decision–making in the European Union is difficult to learn.