By the early 1870s, the term ‘filth’ had become Wagner’s shorthand for Offenbach. He attacked his fellow composer both publicly and privately and sought to establish a polarity between the two, confining Offenbach to the realm of frivolous and materialistic popular folk culture while casting his own work as exemplary of the new German spirit. Laurence Senelick’s close analysis of Wagner’s writings, including his notorious 1869 essay ‘Jewishness in Music’, shows this critique to be fuelled by jealousy, cultural imperialism, and his growing anti-Semitism. Nietzsche is included here as a counterpoint, challenging his former mentor and celebrating Offenbach as the exemplar of Jewish genius. Laurence Senelick is Fletcher Professor of Drama and Oratory at Tufts University and Fellow of the American Academy of Arts and Sciences. His most recent books include Soviet Theater: A Documentary History (2014, with Sergei Ostrovsky) and the second, enlarged edition of A Historical Dictionary of Russian Theatre (2015). This article is taken from his forthcoming The Offenbach Century: His Influence on Modern Culture (Cambridge University Press).