When published, Sartre's Critique of Dialectical Reason appeared to be a major intellectual and political event, no less than a Kantian effort to found Marxism, with far-reaching theoretical and political consequences. Claude Levi-Strauss devoted a course to studying it, and debated Sartre's main points in The Savage Mind; Andre Gorz devoted a major article to explaining its importance and key concepts in New Left Review. Many analysts of the May, 1968 events in Paris claimed that they were anticipated by the Critique. But the book has had a very quiet 50th anniversary: it is now clear that the project has had little lasting effect beyond a narrow band of specialists. It has not entered the wider culture, has not been picked up beyond Sartre scholars except by one or two philosophically interested social scientists and feminist thinkers; and after the energy of 1968 wore off the Critique faded as well from the radar of political activists. This article asks and attempts to answer the perplexing question: Why? What became of the great promise of Sartre's project?