Air pollution has been defined as the presence in the outdoor atmosphere of substances in concentrations sufficient to interfere directly or indirectly with man's comfort, safety, or health, or the full use and enjoyment of his property. The booklet presents information about some of the many factors which influence the nature and extent of the nation's air pollution problems. Included are maps which show graphically major potential sources of air pollutants in the 50 States. Also shown are the activities of governmental agencies toward the goal of attaining more effective control of air pollution.