The paper briefly traces the history of air quality problems in residential, office, and public access buildings to show the evolution of indoor air quality (IAQ) concerns. It then briefly discusses sources of IAQ problems--both known and suspected--then reviews the current state of knowledge of emissions from these sources. It summarizes recent and current research in federal and private-sector organizations. Combustion sources, material source (e.g., building materials and consumer products), activity sources (e.g., cleaning, maintenance, and cooking), and outside sources (e.g., outdoor air, soil gas, and contaminated groundwater) are used as categories to describe the complex problems being researched. The paper concludes with suggestions to building design, construction, and management professionals regarding prudent steps that can be taken to reduce potential IAQ problems from sources of greatest potential concern in today's residential, office, and public access buildings.