Résumé : This PhD thesis contains three analyses: one taking an international approach and two focusing on the Belgian labour market. Using macro-level data for 25 developed countries between 1990 and 2015 and several panel data estimations, the results of Chapter 1 suggest that collective bargaining has a poverty-reducing effect through the interaction between trade unions and the welfare state rather than through its role in wage formation. Using matched employer-employee data for Belgium covering the period 1999-2016, the results of Chapter 2 show that first- and second-generation from developing countries earn remarkedly less than workers born in developed countries (i.e. a persistent intergenerational wage gap). However, most of these gaps are explained by compositional effects (e.g. age, tenure, education and occupation), whose extent considerably varies across generations. Using the same data as in Chapter 2, yet focusing exclusively on tertiary-educated workers, the results of Chapter 3 point out that while immigrants overeducation disappears across two generations among full-time workers, this issue remains intergenerational persistent among part-time workers. Therefore, this PhD thesis provides insightful advice for the implementation of policies and strategies that ensure fair and well-functioning labour markets and social protection systems for people at risk of poverty and/or with a foreign background.