This chapter examines the social dimension of sustainability by situating it within the broader debate on sustainable development and by highlighting the analytical relevance of social capital as a conceptual bridge between social cohesion, equity, participation and collective well-being. While environmental and economic dimensions have historically dominated discussions on sustainability, the chapter shows how social sustainability has progressively emerged as a distinct and complex field of inquiry, shaped by cultural orientations, everyday practices and institutional arrangements. Drawing on recent theoretical developments, social sustainability is conceptualised as grounded in four interrelated pillars—equity, well-being, participation and social capital—whose interactions produce the conditions for inclusive and cohesive communities. Within this framework, social capital is understood not only as a relational resource embedded in networks of trust and reciprocity but also as a structuring factor that enables belonging and democratic engagement. The chapter argues that a social capital perspective allows for an operationalization of social sustainability by clarifying how social systems foster cooperation, reduce exclusion and support shared capacities for shaping the future. It concludes by calling for further empirical work to develop analytical approaches capable of capturing the dynamic interplay between social relations, institutional settings and sustainable development trajectories.