Generalizing theoretical formulation and its empirical test are balanced in the present investigation. With R. K. Merton I regard theories of the middle range as the immediate task of sociological research: generalizations that are inspired by or oriented towards concrete observations. However, the exposition of the theory of social classes and class con?ict stands in the center of this investiga tion. The résumé of Marx's theory of class, the largely descriptive account of some historical changes of the past century, and the eriti cal examination of some earlier theories of class, including that of Marx, lead up to the central theoretical chapters; with the analysis of post-capitalist society in terms of class theory a first empirical test of my theoretical position is intended. The whole investigation re mains in the middle range also in that it is, as its title indicates, confined to industrial society.