The episode of the Bijlmermeer disaster reveals not only the presence of illegal immigrants in Dutch society, but also the authorities’ ignorance with regard to the social composition of the city they administer. These observations arc consistent with van Gunsteren’s (1993) concept of the ‘Unknown Society’ (cf. Habermas’ (1985) ‘N ew Complexity’ (neue Uniibersichtlichkeit) or Beck’s (1986) ‘Risk Society’ (RisikogesellschaftJ). Modern society is less knowable than in the decades after World War II. The policy and implementation designs that authorities and bureaucrats use to interpret and predict social and economic trends in society are no longer in correspondence with what actually goes on. 1 The altered composition of advanced societies, as a result of migration and the differentiation in household forms and lifestyles, and the globalization and informalization of the economy, have contributed to this lack of knowledge. There is a growing discrepancy between the officially documented reality and the undocumented reality.