For the last forty years, the European Union has been pursuing the goal of a unified system of patent law, which would make it possible for an invention to be protected, by EU law, throughout the territory of the Member-States, with a single application. This would simplify the patent protection system, making it easier, less costly and more secure, and would facilitate access to the internal market and promote scientific and technological development. However, problems might arise because of the plurality of legal sources that could be involved and due to the fact that not all countries want to be part of this new system. Nevertheless, the involvement of the majority of the Member-States in the Unitary Patent Package, through participating in an international agreement and in using the EU’s enhanced cooperation mechanism, is evidence of federalist manifestations of the EU as a sui generis organisation.