Nathan Birnbaum (1864-1937), a major but mostly neglected and mercurial figure in modern Jewish cultural history, has been mentioned occasionally, but always briefly, in Kafka scholarship. Usually, it is within the context of Birnbaum’s visit and lecture in Prague, which Kafka attended, or regarding Kafka’s fascination with Yiddish theater and the Yiddish language that the connection between the two has been forged. This lecture claims that Birnbaum’s writings played a major role in mediating a particular view of “Americanism” (“Amerikanismus”) in Kafka’s larger understanding of nationality or nationalist possibilities in general, which in turn exerted an impact in particular on Kafka’s evolving ideas about Jewish nationality. Birnbaum’s views, filtered through the alembic of Kafka’s inquiring mind and his creative literary process,naturally found their way into his writing, for example into the conception of his early novel project set in the U.S., Der Verschollene (Amerika, The Missing Person). The American-Yiddish-Jewish intercultural exchange between Birnbaum and Kafka is an unknown but very telling and important aspect of the background for the development of Kafka’s early thought and writing.