Rudolf Rocker was born in 1873 in Mainz, Germany, and died in 1958 in New York. During his life, Rocker witnessed a rapidly changing world, and he extensively documented these changes. In a microcosm, Rocker's life reflects the development of the various trends within the anarchist movement, of which he was a prominent member. He joined the anarchist ranks at an early age, and to his last breath he remained an ardent believer in the goals and principles of anarchism. Rocker's main philosophical concern had been personal freedoms and the ability of society to protect these freedoms by non-coercive means. Rocker rejected the morality of all forms of authority, whether state, party or privileged minority. The only form of organization condoned by him was that of workers' federations or syndicates. In Rocker's vision, these federations would serve as the basis for creating a federated Europe, and ultimately a federated world order. A disciple of Peter Kropotkin, Rocker established his prominence in anarchist philosophy as the ideologue of anarchosyndicalism, his main contribution being the combination of theoretical anarchist theses with a practical syndicalist platform of action. Rocker's most important contribution to political philosophy, Nationalism and Culture, contains both a comprehensive analysis of the rise of national sentiments, and a theoretical attempt to refute the morality of the state. Rocker left his mark on anarchist history not only as a theoretician, but also as a practitioner. He was particularly active among the Jewish immigrants in London's East End, where he organized a cohesive and militant anarchist group. He led the local workers in industrial struggles against the "sweating system," and for two decades Rocker, a gentile with no knowledge of Yiddish, edited the Jewish anarchist organ, the Arbeter Fraint. In 1923, Rocker became known internationally due to his role in founding the Syndicalist International, the aim of which was to halt the growing influence of the Comintern. Despite his political activities and writings, Rocker's life remained a neglected chapter in the history of anarchism. Drawing extensively on Yiddish sources, this work attempts to save Rocker from his undeserved oblivion.