During the first two decades of the twentieth century, a mass culture of popular radicalism – consisting of various socialist, industrial unionist, anarchist, Progressive, feminist, black radical and other movements – arose to challenge the legitimacy of corporate capitalism in the United States. This article considers the role of radical cartoonists in propagandizing for, and forging unity within, this culture of popular radicalism. By articulating a common set of anti-capitalist values and providing a recognizable series of icons and enemies, radical cartoonists worked to generate a class politics of laugher that was at once entertaining and didactic. Through a discussion of the works of Art Young for The Masses, Ryan Walker's cartoons for the socialist newspaper, Appeal to Reason, and the proletarian humor of Joe Hill and the IWW, this article argues that radical cartooning did not merely provide comic relief for the movements, but was an active force in framing socialist ideology and goals in a revolutionary age.