During the 1970s, governments increasingly expressed concerns about the loss of revenue through the use of tax havens by both individuals and corporations. This article explores a covert international working group (the Group of Four) set up between France, Germany, the United Kingdom, and the United States in 1969 in response to such concerns. At regular meetings, officials exchanged information gathered by their respective tax authorities in auditing multinational companies. In the 1980s, under increasing pressure from governments in a now much more hostile climate to tax authorities, the Group’s work shifted away from multinationals and toward more general, technical questions. The history of the Group of Four illustrates the importance of the 1960s and 1970s as a period for regulating economic actors and the impact of broader circumstances on the success or failure of anti-tax avoidance measures.