The New Left that arose in West Germany during the 1960s mimicked the antifascist reformations of the 1930s. For grassroots campaigns, extraparliamentary opposition groups, and radical student organizations of the postwar decades, the Marxist humanist theories and revolutionary socialist splinter groups of the interwar years served as attractive models. At the same time, the Sixty-eighter generation rebelled against a political establishment now represented by that earlier generation of neoleftist pioneers, their parents. But generational conflict was just the symptom of a deeper problem in the history of the midcentury Left: a succession of radical new lefts arose out of periodic frustration at institutionalized politics. This article explores the missing link between Germany’s antifascist and antiauthoritarian new lefts: the so-called left socialists of the 1950s. In particular, Ossip K. Flechtheim’s science of futurology and Wolfgang Abendroth’s theory of antagonistic society translated antifascism’s legacies into a new paradigm of social protest. The left socialists’ support for the embattled Socialist German Student League laid the organizational and intellectual foundation for the sixties New Left. Recent studies of the “global sixties” have shown the transnational connections between new lefts across space; this article explains their continuity across time.