Before setting out a model suggesting the dimensions of ethical conduct and its assessment in contemporary society, this chapter discusses a number of developments which are of relevance in the construction and application of such a model. All planning can be assessed within a model of rational action, that is, a model relating means to ends. The chapter describes the great extension of conscious collective planning in modern society, whatever its political ideology. Modern society has often been described as the scientific society. Much of modern life has been shaped by scientific discoveries, and many of the cultural heroes are scientists. Human conduct is typically assessed as morally good or bad in the context of an ethically challenging real world situation. After World War Π, social problems associated with slum clearance and public housing construction gradually stimulated a greater interest in the social, economic and political dimensions of urban planning.