In the early 1970s, seven states had lotteries and one state had casinos. Today, some form of legal gambling exists in all but three states. What accounts for this rapid growth in legal gambling in the United States? John Lyman Mason and Michael Nelson tackle this complex question, highlighting two factors to explain gambling's proliferation: the decentralized nature of gambling regulation and policymaking, and the tendency of states to respond to policy changes made by their neighbors. As they appraise the politics behind gambling policy at the state, tribal, and federal levels, the authors detail the influence of interest groups, campaign contributions, and public opinion in bringing about the current wave of gambling legalization. Noting that changes in gambling policy often take place without a careful evaluation of costs and benefits, Mason and Nelson offer a number of recommendations for improving decisionmaking and protecting the public interest.