Reactions among indoor pollutants consume the reacting pollutants and generate new pollutants, influencing the kind and concentration of chemicals in indoor air. In the absence of combustion, such indoor chemistry is the major source of highly reactive compounds indoors. From July 1215, 2004, approximately 70 participants from eight countries met at the campus of University of California, Santa Cruz for a Workshop titled 'Indoor Chemistry and Health' conceived and sponsored by the U.S. National Institute for Occupational Safety and Health (NIOSH) with additional support from the Harvard School of Public Health (HSPH). As implied by the title, the focus of this workshop was adverse health effects that might result from exposure to the products of reactions among indoor pollutants. Scientists from multiple disciplines including chemistry, toxicology, medicine, epidemiology, and public health were enlisted to address this subject.