Without additional immigration of several million people over the next few decades, the demographic development of most European countries will lead to a considerable population decrease. Because such a reduction is neither desirable nor realistically possible, cities in particular will be the target of increasing immigration, and hence will undergo qualitative change. Today, there are large ethnic and cultural minorities in many German cities and suburbs; in the future, whole cities will become international, and suburbs will become ethnic‐cultural communities. This article presents a theory for the discussion on how such a change can be managed productively. The concept of the ‘open city’ is understood as both a risk and an opportunity. This article pleads for a socio‐culturally segregated division of urban space for the prevention of discrimination to be possible. The multitude of separate cultures must be supplemented by a ‘hyper‐culture’ in order to integrate the urban culture as a whole.