This project examines existentialism as a historically relevant and deep-rooted American phenomenon. By triangulating the three geographical points of France, the River Plate region (Argentina and Uruguay), and the U.S. through their literary treatment of existentialism, this study shows how existentialist theories are developed and contested in the work of a number of key writers in the Americas. When approaching existentialist concerns through literature, not only French authors but also U.S. and River Plate writers display distinct existentialist trends that span the entire twentieth century. In order to reveal why the American continents were in fact a natural locus for the development of existentialist thought, I examine a wide array of modernist, post-World-War-II, “post-boom,” and postmodern works that illustrate and challenge some of the shared characteristics that are specific to America as a hemisphere and as a discursive concept. In examining late twentieth-century permutations of existentialism, I also demonstrate how postmodern works sometimes subvert and build on Sartrean existentialist theories through parodic strategies and integrate apparently incompatible postmodern and existentialist insights, developing what we might call a “postmodern existentialism.” Such late twentieth-century transformations of existentialism, I argue, innovate this movement and further reveal the need to study American and postmodern literature as a part of the existentialist canon.