Claims for unemployment insurance (UI) benefits that are payable under regular state programs declined significantly during the 1980s relative to total unemployment. The purpose of this report is to present the results of an extensive study of the resasons for this decline. This study was based on statistical analyses of national data over the 1948 to 1986 period, on analyses of more detailed data from all the states over the 1971 to 1986 period, and on in-person interviews with UI officials in the largest states. In general, the analyses found that no single factor explained the observed decline in UI claims over the 1980s; rather the decline was caused by changes in the general labor market and by a number of policy changes at both the federal and the state levels.