This paper presents an interest group model of gambling regulation and applies it to major changes in the regulation of US gambling markets. Gambling markets are among the most restricted and politicized markets in the American economy, yet economists interested in the economics of regulation have paid them little attention. Applying the economic theory of regulation to gambling markets can lead to greater understanding of current public policy. In addition, this application may shed light on the discipline itself, as to its ability to explain recurrent fluctuations in the extent of regulatory intervention over long periods of time. Broadly speaking, the interest group model is consistent with changes in the extent of regulation, including the recent period of liberalization and consequent growth in gambling.