This volume of the Occasional Paper series presents two studies of interstate competition in the Unemployment Insurance (UI) system. Determining the extent of economic competition among states is an extremely difficult undertaking. The papers in this volume attempt to shed light on this topic and quantify the effects of some aspects of competitive behavior. Using yearly UI state administrative data, Laurie Bassi and Dan McMurrer construct an economic model to explain the change in state UI tax rates and how much interstate competition might be affecting those rates. In the second paper, Wayne Vroman provides a critique of the Bassi-McMurrer methodology and then constructs a different model to measure competitive effects on UI tax rates. Vroman also offers an analysis of interstate competition in the Workers? Compensation Program.