Among the German historians of the period before the second world war, Arthur Rosenberg occupies a unique place, not only because he stood very much on the left, but also because he was very active in politics, as a deputy in the Reichstag as well as a leading functionary of the KPD (Communist Party of Germany) and the Comintern (Communist International). There were a few other left-wing historians (the vast majority of German historians were fairly far to the right), for example Gustav Mayer and Eckart Kehr; but they took no prominent part in political life and were satisfied to make their mark through their writings; their politics, too, were much more moderate than those of Rosenberg, who was not only a leading communist, but also for some time a leader of the ultra-left wing of the party. It is also true, however, that he wrote the books by which he is remembered today-The Birth of the German Republic, A History of Bolshevism, A History of the German Republic, and Democracy and Socialism-after he had broken with the KPD and communism, and had ceased to play an active part in politics. Curiously enough, there was nothing in the first thirty years of Rosenberg's life to indicate a trend to the left or a strong interest in politics. He was born in Berlin in I889, the son of a Jewish businessman and, up to the outbreak of the revolution in November 1918, he led a conventional middle-class life, hardly disturbed even by the first world war and the rise of a radical anti-war movement in Germany. He went to a Berlin Gymnasium, and then studied history and classical philology at Berlin University, devoting most of his time to ancient history. In 9I I he gained his doctorate with a thesis on 'Investigations into the