The authors review a number of studies that have focused on the income gap between the rich and the poor in the United States and discuss the following topics: the relationship between size and availability of economic rewards in American society; economic mobility in the United States; and cross-national comparisons, in which economic mobility in the United States is compared to that of other countries. A table that presents U.S. mobility rates using relative quintile-to-quintile transitions covering various periods from 1967 to 1991 is included, along with an article by the authors entitled, "How Much Do Americans Move Up and Down the Economic Ladder?"