This chapter reflects on the contours of the Rule of Law and how that concept comes to life in the European Union context, especially in the realm of European Competition Law. Departing from a historical perspective, we analyse the intellectual discussion that has always surrounded this principle and the different configurations it has taken on up until the present time. Drawing on the European Court of Justice’s case-law, in particular the Sped-Pro case, we understand the need to extend this principle to national competition authorities, which were traditionally left out of its scope, in order to protect fundamental rights and ensure the enforcement of competition law as an essential objective of the Union.