The purpose of this chapter is to demonstrate that John Stuart Mill’s chief influence on twenith and twenty-first century philosophy of science was through On Liberty. This includes discussions about uptakes of Mill’s ideas in Feyerabend’s relativist and his notion of a ‘Mutual Killing Society’, Kitcher’sKitcher, P. ‘well-ordered scienceWell-ordered science’, and Longino’sLongino, H. contextual empiricism. After clarifying that Mill would not have endorsed the ideology underpinning the ‘marketplace of ideasMarketplace of ideas’ metaphor often used to describe Mill’s views on democracyDemocracy, science, and truthTruths, it is shown the various uptakes and misunderstandings of Mill’s political epistemology in late twentieth century and early twenty-first century philosophy of science. Here, it is shown that Feyerabend originally wrongfully interprets Mill as someone who endorse a ‘Mutual Killing Society’, demonstrating a misunderstanding of Mill’s understandings of utility and freedom. Eventually Feyerabend comes to recognize their differences, where Mill was a realist about truthTruths while Feyerabend was a relativist. However, Feyerabend did enact Mill’s call to proliferate marginal viewpoints with gusto. It is finally shown that Longino has enacted Mill’s call for pluralism both by criticizing dominate androcentric hypotheses and promoting feminist science.