Building capacity to improve health through applying health impact assessment (HIA) increases the range of people, organisations and communities who are able to address health problems and, in particular, the problems that arise out of social inequity and social exclusion. To achieve this, a range of strategies is required across the areas of organisational development, workforce development, resource allocation, leadership and partnerships. A conceptual framework to guide understanding of capacity building evolved during a three-year capacity building project that supported the implementation of HIA. This is also applicable to the broader agenda of healthy public policy.