Social capital is the norms, values, and trust created by a social network. Higher social capital is generally associated with improved physical and psychological health. This thesis explores the relationship between social capital and wellbeing. Chapter one, a systematic review of the literature, examines social capital and loneliness, two concepts assumed to overlap. 15 studies were included in the review, which examined individual structural and cognitive social capital, and their relationship with loneliness, on a global scale. Overall, a weak inconsistent association between the concepts was identified. Due to, primarily cross-sectional methodologies, and the use of non-control group interventions, causation could not be established. These findings cast doubt on the strength of the previously assumed conceptual overlap. The review identified a need for more consistency when defining and measuring social capital. It also identified a need for ecological studies of social capital and loneliness; longitudinal studies; and randomised controlled trials of social capital interventions for loneliness. Chapter 2 is an empirical study, which examined disability group, as a moderator of the relationship between residential churn and psychological wellbeing. Disability group was assigned in terms of functional limitation; and residential churn is a recognised disrupter of ecological social capital. A multi-level analysis identified a relationship between wellbeing and churn, that was dependant on disability. High churn was associated with lower wellbeing for those in all disability groups. However, this was only significant for respondents in the severely limiting disability group. Chapter three discusses recommendations for research and clinical implications of the previous papers. Clinical implications are considered at the individual, organisational, community, and system wide level.