The Environmental Criteria and Assessment Office and the Office of Air Quality Planning and Standards are charged with responsibility for reviewing and assessing air quality criteria and air quality standards, respectively. Since adoption of the 1977 Clean Air Act Amendments, the U.S. Environmental Protection Agency has published criteria documents for all of the criteria pollutants and completed action on hydrocarbons, lead, and ozone standards. Currently ozone and lead documents are again under review, while proposals for carbon monoxide, nitrogen dioxide, and particulate matter ambient standards have been published. The paper summarizes both the basis for existing health criteria and standards and the status of current agency review of the criteria and standards.