This dissertation focuses on the trade-union responses to immigration. Immigrants have long constituted a challenge for labor unions, resulting in a wide variety of union responses historically and cross-nationally, ranging from restrictive and exclusionary policies, to orientations supporting the liberalization of labor migration laws and socio-economic integration. A variety of factors are posited to influence unions response to labor migration and immigrant integration, including the effects of globalization internationalizing labor markets, economic restructuring, porous borders), weakened labor movements, industry characteristics, grassroots activism, and union ideologies. While each of these factors offers important insights, their explanatory value is significantly enhanced by appropriately contextualizing each in relation to the degree to which unions are embedded in institutionalized decision-making and consultation relationships with employers and the state embeddedness). The more embedded unions are in a dense web of multi-level exchange relationships, the more influence unions have in policymaking, but at the same time, more compromise is encouraged among social partners as each issue area becomes part of a larger system of concessions and credits. I argue that the greater the embeddedness, the more unions position on immigration and integration will be homogeneous among unions and will reflect the dominant immigration/integration regime in the country. More specifically, embedded unions are posited to take more conciliatory stances towards employer demands for labor migration in exchange for limiting conditions e.g., equality in working rights) to reduce exploitation and protect domestic wages and conditions. Other integration efforts are more likely to support migrant interests through general, universalized efforts e.g., anti-poverty or anti-discrimination campaigns) than targeted, specialized programs directed specifically at migrants. Conversely, weakly embedded unions will exhibit more variation in their policies towards immigrants given their fragmentation, weaker position in industrial relations and greater susceptibility to changing labor market conditions. With less policy influence, unions are more likely to oppose labor migration. However, in the context of union decline, in unions representing sectors with increasing diversity, there will be greater incentives for the targeted organizing of immigrant origin workers, and for developing more inclusive internal programs and structures to facilitate their integration. Union ideology and grassroots mobilizing are also posited to play a greater influence in determining union commitment to integration efforts. These tendencies are supported by the cross-national comparison of eight countries. Insights from two in-depth case analyses strongly embedded unions in neo-corporatist Belgium； weakly embedded unions in pluralist Canada) further buttress these arguments, as well as providing the relationship between embeddedness and union responses towards immigration and integration with a plausible causal mechanism.