As casinos and other forms of gambling spread across the United States, voters and policymakers are becoming increasingly interested in the potential costs and benefits from expansion in gambling industries. Since the mid-1990s, a variety of cost-benefit research has been published, much of it using flawed methodologies. This paper examines some of the most important areas of debate and disagreement among gambling researchers, and explains why the quantification of the costs and benefits of gambling is problematic.