This chapter engages with the work of Erving Goffman, Ian Hacking, Gil Eyal and Dan Navon to describe the impact of classifications on people and the impact of people on classifications. Goffman described the phenomenon of stigma: how a label becomes part of how you and others understand yourself. Ian Hacking has investigated how classifications alter those classified and how those classified alter the classifications themselves, a phenomenon he calls the looping effect. Gil Eyal and Dan Navon have applied this idea to the association between genetic syndromes and autism. Although the relation between genes and autism seems straightforward – genes ‘explain’ autism – their paper demonstrates that other mechanisms contribute to classifications and objects of study.