This book explores the representation of women and their interests in the world of work across four trade unions in France and the UK. Drawing on case studies of the careers of 100 activists and a longitudinal study of the trade unions' struggle for equal pay in the UK, it unveils the social, organizational, and political conditions that contribute to the reproduction of gender inequalities or, on the contrary, allow the promotion of equality. Guillaume’s nuanced evaluation is a call to redefine the role of trade unions in the delivering of gender equality, contributing to broader debates on the effectiveness of equality policies and the enforcement of equality legislation.