From the mid 1950s to the late 1980s, Ralph Harris and Arthur Seldon, as general director and editorial director respectively of the IEA, battled against a conventional wisdom which was hostile to markets. Eventually, by force of argument, they overcame much of the resistance to market ideas, and in the process established the Institute's formidable influence in shaping both opinion and policy. This Occasional Paper begins with a transcript of a conversation with Harris and Seldon which provides many insights into how they worked and what obstacles they encountered. Eight distinguished scholars, each familiar with the work of the Institute, then provide commentaries which assess its influence on thinking and the challenge to government which it constituted during the Harris/Seldon years.