Based on a field survey carried out in a local CIMADE group located in an average city in the province, this chapter questions the concept of professionalisation with regard to a specific form of work that is usually invisible: advocacy and voluntary work. The observations show that the militant work carried out in these associations — both in nature and in its policy framework — is becoming institutionalised: it is routinely, judicious, individualised and formalised. The growing role of law (envisaged both as a tool and an object) and of the legal defence of foreigners in advocacy requires the acquisition of specific skills, knowledge and know-how. Activists form themselves in law, use a specific vocabulary, and their knowledge and practices become homogenous. It is then the recruitment of activists with a high cultural capital that is encouraged. Lawyers, employees and volunteers, are also numerous activists. This chapter shows the extent to which their individual trajectories combine professionalisation logically, understood in this case as a process of professional stabilisation, and voluntary engagement.