[Truncated abstract] BACKGROUND This thesis explored the relationship between social capital, sense of community and mental health and wellbeing; and factors that may influence these within the environments in which people live. Area variations in health are well documented and are mirrored in emerging evidence of geographic and neighbourhood variations in social capital. Little is known, however, about the specific facets of the impact of local physical environment on social capital; or about the mechanisms by which these are linked with each other, and with health determinants and outcomes. Despite the recent proliferation of social capital literature and growing research interest within the public health realm, its relationship to mental health and protective factors for mental health have also been relatively unexplored. AIMS The overall aim of this thesis was to explore the potential associations between social capital, health and mental health, and neighbourhood environments. In particular, the thesis considered whether the physical attributes and street network design of neighbourhoods are associated with social capital or particular dimensions of the social capital construct. It also examined the relationship between social capital and demographic and residency factors and pet ownership ... CONCLUSION The combined use of qualitative and quantitative research is a distinguishing feature of this study, and the triangulation of these data has a unique contribution to make to the social capital literature. Studies concerned with the measurement of social capital to date have tended to focus on dimensions pertaining to people’s involvement, perceptions and relationship with others and their community. While these constructs provide insight into what comprises social capital, it is clear that each is in turn influenced by a range of other factors. Elucidating what fosters trust and neighbourly interactions in one community and not in another, and by what mechanisms, is one of many research questions unanswered in the published literature to date. The consideration of measures of social capital that relate to the physical environment is therefore of relevance to the growing research and public policy interest in identifying what might build or restore social capital in communities.