The main interest of this interdisciplinary thesis (psychology-law) is the understanding of transphobia and discrimination against trans* people. I locate the problem of this type of discrimination in the social construction of ‘sex/gender’ categories. Particularly, I situate it in the definition of the norms that constitute ‘woman’ and ‘man’ as two essential and mutually exclusive categories that sustain the unequal binary organisation of society. People who transgress those norms have been labelled as ‘mentally ill’ by psychiatry and psychology since the end of the 19th century. The emergence of trans* activism from the 1960s and especially Trans Studies in the 1990s has allowed questioning those pathologising discourses. In the present context, we observe a tendency towards the depathologisation of trans* experiences and identities. Depathologisation is coupled with increased visibility of trans* people in the cultural domain and a more favourable public opinion towards them. However, trans* people still face serious discrimination and the norm that divides humankind into ‘women’ and ‘men’ is still very much present. Drawing on these premises I argue that the transgression of ‘sex/gender’ norms have been redefined nowadays so that the binary opposition between women and men is maintained as the norm. Thus, trans* people are still depicted as ‘abnormal’ although pathologising and psychiatric discourses are not necessarily employed today. The general objective of the thesis is to understand how this redefinition is carried out and the effects of it in two specific contexts: the legal certification of sex in the civil status of individuals in Belgium and the definition of the worker subject. The choice of these two cases responds to the fact that trans* people report facing many obstacles and discrimination in them. Based on the theoretical and methodological principles of discursive psychology and Perelmanian new rhetoric, I realised the discourse analysis of two corpora: a legislative corpus and a corpus of ...