This chapter contains a legal analysis of the regulation of social security rights of trainees in Germany, France, and Spain, three European Union Member States with a system based on professional social insurance. While an extension of social security rights of employees can be observed, the regulation creates situations of segmentation, both among trainees and between trainees and employees. Being paid an allowance of a certain level generally appears to be a decisive factor, which highlights the importance of paid traineeships. Moreover, when there is extension, it does not operate for all social risks, particularly not unemployment. And while traineeships play an important role in EU youth employment policy, EU instruments, like the Quality Framework for Traineeships, do not address those questions adequately. This is to be lamented, as those regulative problems could be considered as contributing to a phenomenon of systemic discrimination against young workers.