This dissertation shows how the intersection between German and Yiddish became an important but largely forgotten site of literary production in the long twentieth century. Beginning in the late eighteenth century, German and Yiddish came to be associated with divergent trajectories of Jewish modernity and were often understood to represent either side of a series of charged dichotomies, such as West and East, Germanness and Jewishness, assimilation and dissimilation. This project complicates this history of divergence by recovering a countertradition of writing in two languages, which, despite their linguistic proximity, have most often been considered apart. I assemble a diverse corpus of archival materials and published texts that reveal the widespread use of these languages in conjunction. I turn particular attention to practices of exophonic (‘nonnative’) writing, translation, transliteration, and commentary in the work of Moyshe-Leyb Halpern, Malka Lee, Franz Kafka, Bertha Pappenheim, Paul Celan, Shloyme Bikl, Yoysef Bernfeld, Freed Weininger, and Chava Rosenfarb, among others. In analyses of their work, I elucidate how their writing practices re- and disarticulate the relationship between German and Yiddish, often in experimental and formally inventive ways. In so doing, I demonstrate how this specific linguistic relationship came to matter in various contexts, including in the development of Yiddish modernism, in feminist efforts to recover women’s history, and in debates about the future of Jewish cultural production in the wake of the Holocaust.