Summary Shadow places. Patterns of spatial concentration and incorporation of illegal immigrants in the Netherlands In western countries illegal immigrants constitute a significant segment of the population. By combining quantitative and qualitative research methods this article describes, and explains, illegal immigrants’ patterns of spatial concentration and incorporation in the Netherlands. So far these spatial patterns have not been described and explained systematically, neither in the Netherlands nor elsewhere. The article shows that illegal residence is selectively embedded in the social structure. Urban and rural concentration areas are often characterized by the (simultaneous) presence of legal family members and countrymen, openings in the labour market, cheap accommodation opportunities, and potential life partners. The authors argue that illegal immigrants are likely to be spatially concentrated and incorporated in other western countries in similar ways; now and in the foreseeable future.