Yiddish and Hebrew writer I. L. Peretz (1852-1915) was a major leader of Eastern European Jewry in the years prior to World War I, and was deeply involved in Jewish politics and communal life throughout his lifetime. In The Radical Isaac, Adi Mahalel examines a central part of his life and art that has often been neglected, namely, his close alignment with the needs of the Jewish working-class and his deep devotion to progressive politics. Although there have been numerous studies of Peretz and his work, this very central component of his life nonetheless remains severely understudied. By offering close readings of the radical Peretz, Mahalel recasts the way political activism is understood in scholarly evaluations of the writer’s work. Employing a partly chronological, partly thematic scheme, Mahalel follows Peretz’s radicalism from its inception and then through the various ways in which it was synchronically expressed during this intense period of history.