Chapter 3 concentrates on a theoretical overview of the concept of social sustainability in several guises. It begins by offering a definition of the concept when it is understood as a quality of communities and societies. It then turns to the sociological literature to explain what is meant by community and neighbourhood, and the importance of face-to-face social interaction in local places for community resilience. It discusses how ideas of social sustainability have been defined and operationalised in research, and social and international development policies. It settles on a version of social sustainability underpinned by ideas of social capital and social cohesion, and reviews classic literature on these concepts. Finally, a case study is offered that shows the intertwinement between forms of social capital and cohesion and collective maintenance of infrastructure in a community in Paraguay, and thus sets up the book’s core argument.