Health insurance markets are regulated by the states under the McCarran-Ferguson Act (15 U.S.C. 1011) of 1945. The ‘purpose clause’ of the Act states that regulation and taxation of the business of insurance by the states is in the public interest. As a result of McCarran-Ferguson, evey health insurer must be licensed in the policyholder’s state of residence. The states have responded with a complex patchwork of mandates and laws that vary widely acrcros the country.