Today, there are still some groups within the European Union integrating faster than others, for example the eurozone and Schengen Area (see: Opt-outs in the European Union).
如今，欧盟内部的集团融合程度也有不一致，例如欧元区和申根区融合进度就较快（参见：欧洲联盟中的退出选择权）。