This chapter introduces the foundational theorists and theories that represent the birth of sociology as an academic discipline. It highlights some of the key ideas of each theorist. Many sociological theories reflect Hobbesian notions of social order, either in terms of conceptualising human nature as self-interested and competitive, or in terms of viewing social order as a human creation and subject to human transformation. The chapter aims to help readers gain an awareness of the range of foundational sociological theories they are likely to encounter in the wider literature. Like many other social scientists of the nineteenth century, Karl Marx also believed in social evolution. He was interested in the major changes brought about by the Industrial Revolution and argued that the way in which goods are produced in society affects everything else. In capitalism, according to Marx, there are two classes of people: the workers and the capitalists.