Health impact assessment (HIA) has many advocates for its use to identify and optimize the health effects of non-healthcare interventions. It is an assessment of the health effects, positive and negative, of a project, programme, or policy. Expertise developed in the United Kingdom from a realization that health impacts are often overlooked during the planning stages of development projects but prior planning can avoid detrimental effects. Considering health impacts is now recommended in all continents; the focus has moved from less to more developed countries and upstream from projects to policies. Health impact assessment shares certain concepts and methods with risk assessment, environmental impact assessment, strategic environmental assessment, social impact assessment, and economic assessments. This paper describes the development of health impact assessment and its relation to these other forms of impact assessment.