In the early nineteenth century it was not at all evident what kind of a science, if at all, political economy was supposed to be. Writers of the discipline attempted to establish themselves as members of a scientific field, while being attacked by socialist and working-class opponents for being capitalist interest disguised as science. Drawing on material from the working-class periodical literature and private correspondences of the political economists in Britain and France, this chapter explores the struggle over the scientific status of the political economists in the 1820s to 1840s. By comparing the debates across the Channel the chapter shows both the national differences and the border-crossing inspirations for the political economists and the socialist movements alike. The chapter argues that the struggle over the status of political economy in this period needs to be understood as a struggle between competing economic rationalities. This struggle was instrumental in the lasting theoretical cooperation between French and British liberal economic thinkers, who aimed at placing the principles of unhindered trade at the basis of any acceptable economic policy.