He came from a middle-class family, which had got poor. He pursued studies of law at the universities of Wien and Budapest, and his statistical and librarian works were outstanding in that period. He took his doctorate in 1899. After some years of practice, he was appointed to the Metropolitan Library, and he became its director in 1911. He planned a comprehensive cultural system. The start to expand library network was according to his ideas. He made an effort to make the services of the institution available for the masses, with special regard to the socially handicapped. The British public library system served as a model. The type of the resource library in (modern) social science was created under his control. He started his scholarly activities in 1903. From 1906 on, he was the vice-president of the Society of Social Sciences. He regularly gave information about the international working-class movement in the periodical 'Twentieth Century'. He wrote articles in the German 'Neue Zeit' and the French 'Mouvement Socialiste' periodicals. He got in touch with Sorel, Kautsky, Mehring, Plehanov and - in Paris, at the end of 1904 - with Lagardelle and the French syndicalists. He got in touch with several Russian socialists as well, who lived in exile. In the years of World War I, despite his serious illness, he became the spiritual leader of the antimilitarist movement. He finished his great historical work 'Social and Party Struggles in The Revolution of 1848-49' in his sick-bed.