This digest of ordinances of selected metropolitan communities, primarily with a population of over 50,000, illustrates the various and divergent approaches followed in dealing with air pollution problems. The 107 ordinances reported emphasize the importance of developing standards, codes, rules, and regulations governing the emission of air pollutants on the basis of technically accepted criteria, and on a consideration of local conditions,such as topography, meteorology, industrial development, degree of organization, and land-use planning.