In 1968, California Governor Ronald Reagan's second year in office, the imprisonment rate in the State's institutions was 146 per 100,000 residents. In 1972, California's State prisons incarcerated 96 prisoners per 100,000 residents - a decrease of 34 percent and the State's lowest level of imprisonment since at least 1950. This study examines how this reduction was accomplished during the tenure of a governor elected in part because of his tough approach to crime and disorder. The authors find that the decrease in the prison population resulted from a confluence of events, rather than a single dominant cause, and that this process extended over a period of years, rather than being limited to Reagan's first year or two in office. There are lessons of value in this history for California's and other States' current problems with high imprisonment rates. However, differences in law, in the scale of imprisonment, and in the politics of penality are likely to limit efforts to substantially reduce prison populations in California and elsewhere. (Published Abstract)