Phenomena of attributing value to objects, practices, and people, and of assessing their value have become a popular subject in sociological research. Classification, among other valuation practices, represents a central topic in these studies. Thus, the sociology of valuation is emerging as a new field that, however, lacks common ground in theorizing about its subject even though preoccupation with valuation has a long-standing history in sociology. Authors such as Durkheim, Simmel, and Dewey have interpreted valuation as more than a specific localizable phenomenon, in that valuation is a constitutive element of the fundament of the social. Discussing classical approaches to valuation and relating them to current sociological work, we identify key concepts within different theoretical approaches that need to be taken into account when theorizing valuation. We suggest five building blocks – valuation practices, value structures, valuation infrastructure, valuation situations, and reflexivity of valuation – theories of valuation need to consider for coming to terms with the multifaceted empirical studies in the sociology of valuation.