This chapter introduces the theory of relation as a new framework for interpreting social phenomena through relation in circulation. With the expression through relation, the theory of relation differs from other relational sociologies that understand society as a relation or a set of social relations. While the theory of relation agrees with other relational sociologies that relational events are at the core of sociological enquiry using a relational scheme, it also differs from these relational sociologies in terms of its basic assumptions. It underlines its difference with its concept of relational structure understood as a deviation from an ideal relation, whose formal and structural formulation is subverted by the primacy of circulation, according to which the theory of the relation fundamentally argues. In this chapter, the authors provide a starting point for understanding core concepts of relational sociology in a new way, like the inscription of human and non-human actors in social relationships, their resistance in opposition or in support of orders of social relationships, and the corresponding new understanding of reciprocity that the theory of relation promotes.