The treaties will enable law enforcement agencies to cooperate across national boundaries to investigate and prosecute crimes. The first MLAT was negotiated with Switzerland and signed in May 1973. The treaty derived from the concern of the United States and Switzerland that organized crime was using Switzerland's banking secrecy laws to hide money obtained from criminal operations. In 1982, the two parties entered into a further agreement enabling the Securities and Exchange Commission to have access to information relevant to investigations of violations of American insider trading laws. Additional MLAT's have been negotiated and signed with Turkey (extradition), Colombia (drug trafficking), the Netherlands (tax haven problems in the Netherland Antilles), Italy (extradition, freezing of assets, and international subpoena power), and Morocco (confiscating narcotics-related assets). Additional MLAT negotiations have been conducted with Canada, Spain, Germany, Sweden, Thailand, Jamaica, Panama, the Bahamas, and the Cayman Islands. The article discusses the substantive issues of negotiation with each of the countries. The author estimates that the United States will enter into many more MLAT's in coming years to combat problems of international drug trafficking and tax evasion. 90 footnotes.