This paper reports on a demographic study that focuses on the patterns of migration to and from specific metropolitan areas which contribute to nonmetropolitan growth and decline. For background, the paper examines some general properties of the United States migration system. Then the concept of metropolitan areas as redistributors of population is developed. A distinction is made between inmigration and outmigration from within a specified field, or population area. It is shown that the very largest metropolitan areas contributed to nonmetropolitan population turnaround in the 1960s because of their early arrival at a net outmigration state, although smaller metropolitan areas also played a role in outward redistribution of population. (Author/APM)