This essay aims to examine the role of ideas and interests in political economy by drawing mainly on theories developed by Karl Marx and Max Weber. The two authors have very different opinions on the drivers of historical development, the establishment of capitalism and the structure of modern society. Marx's notion of historical materialism emphasizes the role of material interest in constructing the boundaries and structure of political economy. Max Weber's notion of the Protestant ethic emphasizes the role of ideas and norms in shaping rational action and modern society. This essay will explore, compare and discuss these two authors and their opinions. Initially I will give brief definitions of the concepts of interests and ideas. The underlying ontological debates regarding the formation of these concepts will be avoided and the boundaries of the concepts will instead evolve over the course of the essay. Secondly, I will examine the role of interests in Marx's theories by examining his notion of historical materialism, his structure of society and Marxist theories of the state. Third, I will compare Marx's theories with Max Weber's notion of the process of rationalization, his structure of society, and the Protestant ethic. The concept of interest will be defined here as the real material needs or desires of the main actors, including individuals and people. groups, in society. (Hall, 1979, p. 176) The concept of ideas will be defined here as a mental representative image of some object. (Audi, 1999, p. 411)Marx and the role of interestsMarx begins his notion of historical materialism by distinguishing the existence of humanity from that of animals by the fact that humanity produces its own means of subsistence. This is what he calls... half the paper... and the spirit of capitalism London: Routledge ClassicsDas, J.R. (2006) 'Marxist Theories of the State' In: Pressman, S. (2006 ) Alternative Theories of the State of New York: Palgrave MacmillanHall, P.A. (1979) "The Role of Interests, Institutions, and Ideas in the Comparative Political Economy of Industrialized Nations" In: Lichbach, I.M. and Zucker-man, A. (1979) Comparative Politics: Rationality, culture and structure Cambridge University PressBecker, S. O. and Woessman L. (2009) 'Was Weber wrong? A human capital theory of Protestant economic history' The Quarterly Journal of Economics 124(2) pp. 531-596Habermas, J (1975) 'Towards a reconstruction of historical materialism' Theory and Society 2(1) pp. 287-300Vanberg, V and Buchanan, JM (1989) "Interests and theories in constitutional choice" Journal of Theoretical Politics 1(1) pp. 49- 62