Despite the fact that immigration policy is today one of the most salient political issues in the OECD countries, we know surprisingly little about the factors behind the very different choices countries have made over the last decades when it comes to immigrant admission. Why has the balance between inclusion and exclusion differed so much between countries - and for different categories of migrants? The answer that this book provides is that this is to an important extent a result of how domestic labour market and welfare state institutions have approached the question of inclusion and exclusion, since immigration policy does not stand independent from these central policy areas. By developing and testing an institutional explanation for immigrant admission, this book offers a theoretically informed, and empirically rich, analysis of variation in immigration policy in the OECD countries from the 1980s to the 2000s.