In spite of decades of scientific research and policy-making, immigrant integration has remained an issue that defies a clear definition. There has been constant, growing disagreement about what immigrant integration actually means. Does it mean integration, emancipation or adaptation? Does it involve minorities, ‘allochthonous’, or foreigners? Does it refer to social-economic factors or socialcultural factors and what would be relation between these factors? Does it mean that the Netherlands has become a multicultural society, or does it rather mean that such a prospect of multiculturalism has to be averted? Different ways of defining and understanding immigrant integration have led to different types of research and various policies over the past decades. However, controversy has persisted on the question of what immigrant integration actually means. Various research and policy paradigms have come and gone, but no single paradigm has been so convincing that it persisted for more than a decade or so. This makes immigrant integration an intractable controversy (Rein & Schön, 1994) or a ‘wicked problem’ (Rittel & Webber, 1973).