This chapter deals with the most “elementary” entities of the static ontology I propose. The choice to begin with this static aspect is explained by the desire to address from the outset the question of the specificity of the social sciences, which study activities involving human beings, i.e. particular beings. I will examine the status that can be given, from the point of view of these sciences, to members of the human species, to animals, to objects, but also to cognitive and discursive entities. This chapter presents categories and their definitions, but also leaves open questions such as the status of animals and, more generally, of living beings. It includes a dynamic dimension in that I propose to dissociate entities from their status in interaction, i.e. in a process. The statuses are those of resource, constraint, stake or interaction partner, with a distinction for resources between the instrumental aspect (interacting with entities considered as resources) and the coordination aspect (interacting with entities considered as interaction partners).