Indoor air quality (IAQ) is a major concern to businesses, schools, building managers, tenants, and workers because it can impact the health, comfort, well-being, and productivity of the building occupants. OSHA recognizes that poor IAQ can be hazardous to workers' health and that it is in the best interest of everyone that building owners, managers, and employers take a proactive approach to address IAQ concerns. This OSHA guidance publication on IAQ provides practical recommendations that will help prevent or minimize IAQ problems in commercial and institutional buildings, and help resolve such problems quickly if they do arise. It provides flexible guidance to employers to help them keep their buildings free of pollutants or conditions that lead to poor IAQ. It also provides information on good IAQ management, including control of airborne pollutants, introduction and distribution of adequate make-up air, and maintenance of an acceptable temperature and relative humidity. Temperature and humidity are important because thermal comfort underlies many complaints about "poor air quality." In 1998, OSHA conducted a series of three workshops on this issue and the proceedings of these workshops were published in 1999. This publication is directed primarily at employers, building owners and managers, and others responsible for building maintenance, but may also be used as a basic reference for all those involved in IAQ issues. Furthermore, information presented here can help with the decision of whether or not the services of an outside professional may be needed. The advice of a medical professional should always be sought if there are any immediate health issues. Contractors and other professionals (e.g., industrial hygienists or other environmental health and safety professionals) who respond to IAQ concerns, as well as members of the general public, may also find this information helpful.