This thesis investigates the political import of economic theory and analysis within German social democracy. Part I (Ch. 1) briefly discusses the Lassallean origins of social democracy with reference to Lassalle's economic doctrines. It continues (in Ch. 2) by analysing the prime contribution of Marx's Capital to shaping the Marxism that displaced Lassalleanism, and came to be embodied in the Erfurt Programme. as the SPD's official doctrine. The main results of my research, however, are presented in the four chapters of Part II. Here, I approach the Political logic and influence of economic theory, by way of case studies of four politically influential social democratic economic theorists: Karl Kautsky; Parvus; Rudolf Hilferding; and Rosa Luxemburg. In addition to developing the main theme of this thesis, each of these may be taken as a contribution to the literature on these particular theorists, as well as to the historiography of German social democracy (in particular, in the period 1890-1914). Marx's Capital was the basis of social democratic economic theory in the period under consideration. Consequently, analysing the development and political implications of social democratic economic theory contributes to the study of the appropriation, interpretation and influence - the 'Rezeption', in short - of Capitol. Moreover, in so doing, I attempt to provide a theoretical critique, and to indicate the actual content as well as methodological shortcomings, misinterpretations and lacunae in the social democratic 'Rezeption' of Capital. My theoretical critique is undertaken from a 'fundamentalist' interpretation of Capital, and illuminates the theoretical limitations - together with the political implications - of the most advanced attempts to move beyond the Erfurt Programme towards a scientific guide to political action in the imperialist epoch. Finally, this thesis is also intended as a minor contribution to the political reading of Capital.