The idea has gotten traction ahead of Saturday's EU summit as a way to allow the union's members to integrate at paces they are comfortable with. But it's a contentious issue.
Historically enemies, minorities and parties like France's National Front are increasingly in sync as the former seek insurance against radical Islam and the latter tries to gain mainstream credibility.
With right-wing parties set to do well in elections in the Netherlands, France, and Germany this year, many are concerned about a Europe-wide populist swing. But the EU remains popular.
As the world's elderly population grows, it is also becoming increasingly urban. But city living poses many challenges to older people. In Manchester, England, they're trying to fix that.