This work offers a comprehensive reading of Hacking's project on making up people. Making up people refers to practices involved in the scientific classification of people, which may implicitly assume or foster the existence of human types. Hacking's works on human kinds have been presented in a fragmentary manner for over the last 30 years. Some of its central notions, such as "human kind" and "looping effects", have been critically received as stand alone notions within the debate between social constructivism and scientific realism concerning psychiatric categories. Despite his critical stance on social constructivism and his proposed reconciliation between social constructivism and scientific realism, Hacking's work has been read as a challenge to scientific realism. Hacking's account of human kinds in terms of the presence of looping effects, alongside his analyses of various classifications that have been revised and ultimately abandoned in the history of psychiatry, have contributed to that interpretation. Hacking's MUP, however, addresses the way in which the scientific classification of people works, rather than whether mental illness classifications are founded in nature or not. By focusing on classification from a historicist stance, Hacking is able to reconfigure the philosophy of the sciences in a distinct and unprecedented manner, presenting an original account on historical epistemology and ontology. It is not one argument, but a comprehensive reconfiguration of the philosophy of the sciences, which allows Hacking to go beyond the divide between scientific realism and social constructivism. This work brings together a larger set of notions to characterize Hacking's account of MUP, makes explicit the philosophical background on classification that supports it, and explores relevant connections to other aspects of Hacking's work, remarkably, his alternative project on the Styles of Scientific Reasoning. On the basis of such a comprehensive reading, it responds to four representative criticisms. By assembling the elements of Hacking's MUP in a comprehensive and consistent picture, this work shows the extent to which it represents a major contribution to the philosophy of the sciences, introducing a distinct approach to the analysis of scientific concepts and a novel vision of the human sciences.