 If authenticity is the category by which I am able to think about what it means to “exist,” then the account of authenticity cannot neglect the social, historical, and political aspects of that existence. Thus it is not merely because twentieth-century existentialism flourished at a time when European history appeared to collapse and political affairs loomed especially large that existential philosophers devoted much attention to these matters; rather, the demand for an account of the “situation” stems from the very character of existence itself, which, unlike the classical “rational subject,” is what it is only in relation to its “time.” This is not to say, however, that existential philosophers are unanimous in their account of the importance of historical factors or in their estimation of the political in relation to other aspects of existence. Emmanuel Levinas, for example, whose early phenomenological work belonged within the orbit of existential philosophy, opposed to the “horizontal” temporality of political history a “vertical” or eschatological temporality that radically challenged all historical meaning, while Sartre, in contrast, produced a version of Marxist historical materialism in which existentialism itself became a mere ideology. But we cannot stop to examine all such differences here. Instead, we shall look at the positions of Heidegger and Sartre, who provide opposing examples of how an authentic relation to history and politics can be understood.