This thesis looks at the use of ‘American Dream’ language by the U.S. labour and civil rights movements during the first three decades following the Second World War. It examines, in particular, the use of such language by socialists and social democrats in three separate, unsuccessful, attempts to transform postwar American society along social democratic lines. While the limits of social democratic and other leftist efforts in and beyond the postwar period has been the subject of significant scholarly enquiry, the use of ‘American Dream’ language in these efforts has, for the most part, been neglected. The thesis begins by offering a definitional analysis of the ‘American Dream’, and suggests that it is an ideology that is built on the premise that the United States is the land of opportunity because of its capitalist system. Whereas the conventional wisdom emphasizes the flexibility and political capaciousness of the ‘American Dream’, this thesis argues that such capaciousness is overstated in the existing literature, most of which pays insufficient attention to the ideology’s relationship to capitalism. The empirical chapters test this claim through an examination of the meaning and role of ‘American Dream’ language in the three cases. Drawing from archival research, and using the analytical lens of the social movement framing perspective, the thesis explains how movement actors in each case invoked the ‘American Dream’ in hopes of redefining its hegemonic meaning, from one that legitimized, to one that fundamentally challenged, American capitalism. It also considers how and why those efforts were unsuccessful. This is done through an exploration of the decision-making processes leading to the movement actors’ use of ‘American Dream’ language, and by examining the nature of the failed attempts to mobilize around their redefined American Dream. The thesis finds that a common source of constraint on these movements in all three cases was the conflation of ‘Americanism’ and capitalism, and its pervasiveness in American political culture. In addition to casting doubt on the conventional wisdom surrounding the ‘American Dream’, the thesis also has implications for some of the broader debates about the impact of American political culture on the American left.