We trace the formation of the Kadehine, a Mauritanian cultural and political movement of the late 1960s and early 1970s, with a focus on aspects of the “political underground” central to the movement’s strategies and organizing principles. As an anthropological history of the Kadehine, we focus on the organizing perspective afforded by its sources (largely interviews and movement literature). These sources emphasize the importance of clandestinity, as well as the influence of New Left ideas. We then develop a concept, “political underground,” describing the importance of clandestinity and its relationship to the radical politics of its time.