Immigration has become a hot topic in West European politics. The factors responsible for the intensification of political conflict on this issue are a matter of considerable controversy. This holds in particular for the role of socio-economic factors and of radical right populist parties. This article explores the politicization of immigration issues and its driving forces in the electoral arena. It is based on a comparative study using both media and manifesto data covering six West European countries (Austria, France, Germany, Netherlands, Switzerland, and the UK) for a period from the early 1990s until 2017. We find no association between socio-economic factors and levels of politicization. Political conflict over immigration follows a political logic and must be attributed to parties and party competition rather than to ‘objective pressures.’ More specifically, we provide evidence that the issue entrepreneurship of radical right populist parties plays a crucial role in explaining variation in the politicization of immigration.