This chapter focuses on Aron's contribution to ‘end of ideology’ theory. Aron played an important role in reorienting the Congress for Cultural Freedom towards this theme in 1955. But, as this chapter shows, the possibility of a post-ideological politics had interested him since the late 1920s. The chapter thus begins by explaining how and why Aron came to be preoccupied with this theme via his involvement in the overlapping peripheries of neosocialist and neoliberal thinktanks in the interwar years. It then considers how his involvement in these circles informed Aron’s writings on the theme of post-war economic planning in some of his writings in the 1940s. After discussing Aron’s involvement in the ‘end of ideology’ debate within the Congress for Cultural Freedom, the chapter considers the implications of this debate for Aron’s views on decolonization, challenging the view that Aron was the theorist of a ‘liberal retreat from empire’. Finally, it considers how Aron’s dissatisfaction with the end of ideology, together with the emergence of the New Left, led him to become increasingly concerned with the need for a revival of normative political theory in the later 1950s.