We open this chapter by recapping some of the main features of modernity in order to understand how key founding sociologists shaped theories in response to this new society. Focusing throughout on social structure, the chapter asks how far sociologists have been able to sustain a belief in social progress backed by scientific knowledge. We see how deep-seated doubts about the consequences of modernity in the twentieth century replaced earlier optimism. Finally we discuss current theories which claim that sociology must once again come to terms with a profound transition to a new society: that is, the emergence of postmodernity.