The monitoring of ambient air quality is of paramount importance for determining ambient levels of pollutants so that they can be related to adverse effects on man and his environment. The considerations and objectives for designing and implementing an air quality monitoring network are reviewed. The types of air monitoring activities are discussed covering permanent fixed site (trend) monitoring, ambient source-linked monitoring, exposure monitoring, and biological monitoring. The components of an ambient air quality monitoring network are reviewed and evaluated along with the quality control program necessary to assure that the date and supporting information are legally and scientifically defensible.