Across Western Europe, the rise of atypical employment has deepened insider-outsider divides. This book asks why two structurally similar countries - Portugal and Spain - pursued different routes to reduce labour market segmentation following the conclusion of the sovereign debt crisis. It argues that the composition of the governing social bloc drives the orientation of reform, while the choice of decision-making arena (parliamentary law-making versus tripartite social concertation) and the EU's evolving social governance shape the breadth and depth of reform. Building on the distinction between competitive and inclusive solidarity, the book compares four domains: employment protection and collective bargaining; statutory minimum wages; regulation of ride-hailing platforms in passenger transport; and the regularisation of precarious public sector work. The analysis covers Portugal's progressive cycle (2015-2021) and Spain's coalition years (2019-2025), drawing on elite interviews, content analysis of parliamentary debates and media coverage, and official documents. The findings reveal a targeted, outsider-focused strategy in Portugal and a more universal re-regulation in Spain. Governing Solidarity offers a fresh framework and rich evidence for scholars of political economy and industrial relations, as well as advanced students and policymakers confronting labour market segmentation.