The report summarizes information on emissions from light-duty vehicles. The report contains the findings and results of three exhaust emission surveillance programs conducted by the EPA: (1) the Great Plains (Two-City) Surveillance Program - 1968-1969 Model Year Survey; (2) the National Surveillance Program - 1970 (Six City) and 1971 (Four City) Model Year Surveys; and (3) a study of emissions for Light-Duty Vehicles in Six Cities - 1957-1971 Model Year Survey. Hydrocarbon and carbon monoxide emmissions for the vehicles tested were assessed by comparing their mean emission levels with applicable Federal standards. In an effort to assess the extent to which local climate, terrain, driving practices and other geographically differentiated factors affect emissions, vehicles were sampled in cities selected to span the range of such factors.