The figure of amicus curiae in the law of the European Union does not allow and has not even foreseen up to now the participation of a subject/subjects outside of a dispute, but with their own legal interest to participate as amicus curiae. The Court of Justice of the European Union does not allow the possibility of participation in a figure that only allows the intervention of subjects other than states and institutions, which are pre-established by Article 40 of the Statute. According to the procedural rules of the Union, the observation of a series of elements testify that such a figure is also obvious but often necessary on some disputes such as those relating to technical matters, such as competition and the environment. The practice up to now has shown that the intervention is used by associations that carry general and legal interests allowing the performance of the function of amicus curiae in a rigorous manner within the limits of this figure. This work, based on a more jurisprudential practice, tries to reconstruct such institute in a comparative way also through other supranational courts, thus regulating the insertions of the amicus curiae to the judges of Kirchenberg.