Class refers to a stratification system that divides a society into a hierarchy of social positions. It also identifies a particular class position using terms such as “lower class,” “working class,” “middle class,” “upper class,” “elite,” or other such designation. The theories of class exist in sociology within the larger topic of social stratification and are based on the works of Karl Marx and Max Weber, as well as the writings of other prominent social theorists who have contrasted, debated, explained, and elaborated the theories of these foundational figures. Students of sociology are introduced to the conceptualizations, research methods, and applications that have advanced and constrained class studies in the United States and around the globe.