The Clean Air Amendments of 1970 (P.L. 91-604) contains a large number of regulatory approaches designed to operate separately and in combination to improve air quality, thereby protecting the Nation's public health and welfare. These approaches include attainment of National Ambient Air Quality Standards (NAAQS) through State Implementation Plans, control of stationary sources, and control of mobile sources. The paper discusses the essential provisions in each regulatory approach so one can appreciate its underlying purpose and the rationale for the Environmental Protection Agency's (EPA) regulatory actions in each area. Air monitoring constitutes one of the most important yardsticks available for judging the effectiveness of regulatory approaches. The paper focuses on one regulatory approach-control of air pollution through State Implementation Plans-depicting it as a feedback control system. The NAAQS are inputs to the system, the Plans are the control mechanism, and air monitoring is the 'feedback loop' by which to guage compliance with the NAAQS. Within the feedback loop are six component subsystems: monitoring site selection, sampling frequency, measurement methods, reference materials, data acquisition, and data analysis and presentation. The paper briefly describes the general operations and scientific requirements of each subsystem. (Copyright (c) Gordon and Breach Science Publishers Ltd., 1977.)