This article explores the differences in unionization rates between migrant and native‐born workers in 23 European countries. It explores whether individual characteristics or contextual factors explain the variation across countries in the degree of trade unions’ inclusion of migrant workers. The analyses show that individual characteristics cannot explain the variation in the difference between migrant and native unionization rates. Characteristics of the industrial relations regime in the country of destination, in particular the institutional embeddedness of trade unions, affect the likelihood that migrants join trade unions as compared to native workers.