Ian Hacking argues that classifications of people are not passive descriptions, because they can change the people classified and thereby transform the classifications themselves. His central claim is that human kinds are “moving targets”: once a category such as multiple personality, autism, obesity, criminality, or child abuse enters scientific, medical, bureaucratic, or popular use, people may begin to understand and experience themselves through that category. Hacking calls this process “making up people,” while the reciprocal transformation between classification and classified person is the “looping effect.” His framework includes five interacting elements: classifications, the people classified, institutions, knowledge, and experts. These elements show that categories do not operate merely as names; they are embedded in clinics, schools, statistics, social services, professional discourses, and public identities. Autism provides a key case: before its clinical naming, autistic people may have existed, but autism was not yet available as a recognised way of being a person. Later, the emergence of high-functioning autism and Asperger’s reshaped both self-understanding and expert classification. Hacking also identifies engines of discovery, including counting, quantifying, creating norms, correlating, medicalising, biologising, and geneticising. These engines produce knowledge, but they also help constitute new kinds of persons. The conclusion is that human classifications are dynamic: they organise people, but people also react, adapt, resist, and remake the classifications that define them.