Learning by doing: the value of case studies of health impact assessment.

The nine health impact assessment (HIA) case studies in this issue represent a considerable contribution to the HIA literature and provide a number of lessons. These lessons include the value of using evidence in HIA to aid decision-making; the various forms that stakeholder and community involvement in HIA can take; and the fact that HIA can act as a catalyst for intersectoral engagement. They also highlight challenges faced by HIA practitioners, including time, methods of assessment, developing evidence summaries and considering equity.