In Chapter 4, Making up people. A project of more than three decades, I present the notions Ian Hacking uses to work in the human sciences. Hacking defines himself as a dynamic nominalist, insofar as he is interested in the interaction between classification and the classified individuals, and he vindicates Michel Foucault as antecedent of this nominalism, being interested in the essential role of history in the constitution of its objects, people and forms of behavior. Hence his idea of historical ontology, which deals with the ways in which the possibilities of choice and of being emerge from history and from making up people, that is to say, the ways in which a new scientific classification can make a new kind of people emerge. This interaction between classification and the classified individual results in what Hacking calls the looping effect of human kinds. But making up people, besides, takes place within an ecological niche. Given that in the kinds of the human sciences the aforementioned loop effect presents itself, Hacking proposes the existence of different classes of kinds. In order to illustrate this, I recuperate Hacking’s work process on this matter, departing from his original question about whether kinds of people are natural kinds.