For some time now, Rotterdam has actively portrayed itself as a policy laboratory. This laboratorial rhetoric, as one could call it, has prevailed in the fields of housing, urban problems and welfare provision, and most recently it has also emerged in the context of Rotterdam as a 'smart city'. The latter is nothing special, as technological applications to urban problems are full of 'urban labs', of experimentation and of what Halpern et al. (2013) have called 'test-bed urbanism'. However, in the context of urban and social policies in a very general sense, it is less common today. To understand the development of governing diversity in Rotterdam, it is pertinent to scrutinize the character and historical roots of Rotterdam's laboratorial logic. The consideration of the city as a laboratory goes back to the Chicago School, many of whose foremost sociologists considered Chicago a laboratory. While they productively wavered between regarding the city as a field site (in which reality was found) and a laboratory (in which reality was made) (Gieryn 2006), the use of a laboratorial rhetoric by policy makers and politicians is of another kind. It is first and foremost a governing rhetoric, which explicitly assumes that urban reality can be made because it is found to be in a certain, more often than not deplorable, state. In Rotterdam, the laboratorial rhetoric has been associated with the 'innovative' character of policies regarding crime, urban segregation and poverty (Noordegraaf 2008). In no small measure, the 'innovative' nature of, for instance, combinations of care and control in social policies have been applauded by scientists (Notten 2008; Tops 2011).