The growing significance of neighbourhoods in the urban planning discipline, alongside increasing attention to the social dimension of sustainable communities and societies, has brought to the fore the need to conceptualize socially sustainable neighbourhoods. In this article we reflect critically on the concept of socially sustainable neighbourhoods in two areas, namely definition and operationalization. We then propose a tripartite framework for measuring social sustainability of urban neighbourhoods, which combines the three elements of neighbourhood, neighbouring and neighbours. This framework is tested, examined and discussed for the case of Bethnal Green, London. We then integrate our findings into a social sustainability enhancement index, which encompasses practical recommendations to promote the social sustainability of Bethnal Green. We conclude this article by highlighting the research and policy implications of the proposed framework, and making suggestions for improving the methodology of future research.