Social capital (SC) is highlighted as an important factor for post-crisis mental health outcomes. However, the heterogeneous nature of the construct makes it difficult to get a clear picture of the evidence concerning the association between SC indices and mental health. This review examines how SC is conceptualized and measured, and the relationships with other variables in quantitative empirical studies investigating the associations between SC and mental health in post-disaster and post-conflict contexts. It includes primary data studies focusing on this association in civilian populations. Studies were identified by searching electronic databases, bibliographic mining, cited reference searching, and personal contact with experts. In total, 15 studies were included: 12 in post-natural disaster contexts and 3 in conflict-affected settings. Findings suggested that individual cognitive SC had an inverse association with post-traumatic stress disorder, anxiety, and depression, and that ecological cognitive SC was positively associated with mental well-being. Individual structural SC (in the form of community networks) may be psychologically protective. However, most of the evidence was cross-sectional, limiting conclusions about causal relationships. More clarity and consistency is needed in the conceptualization and measurement of SC in order to inform post-crisis mental health interventions. (Disaster Med Public Health Preparedness. 2018;12:791-802)