This chapter completes the trilogy of possible starting points for ontology construction, namely relations. In the course of their activities, persons establish relations with other entities. The relations are more enduring than the interactions. Relations with entities considered as resources take all socially constituted forms of right of use, access or appropriation. The relations between persons are reciprocal commitments based on interactions that emerge from interactions, most often in specific social contexts, collective activities, the presence of intermediaries or common issues.