Abstract This analysis focuses on the system of appointments of independent authorities as a key to their proper functioning within the democratic constitutional state, based on the Spanish experience and bearing in mind the particularities of the European constitutional context in which these institutions are rooted. To this end, we first refer to the premises underlying the creation of the various authorities. We then set out the measures used to guarantee the independence regarding the appointment and dismissal of the members of these bodies and, finally, we examine the recent problem concerning the renewal of the heads of the Spanish Data Protection Agency, due to non-compliance with the appointment procedure. Finally, the case of the AEPD allows us to examine the effectiveness of certain remedies arising from the court’s intervention with the help of European law.