This study deals with the essential facilities doctrine in competition law. The purpose of the doctrine is to impose upon an undertaking in possession of an important and unique facility a duty to give access to the facility to other undertakings which cannot pursue their own activity without such access. The article aims at comparing the highlights of the doctrine under US and EU competition law. It analyses how the doctrine emerged and has been applied by the Supreme Court and the lower courts in the United States, which conditions trigger the duty to give access under US law and the importance of the cases involving intellectual property rights. The author turns then to examine in the same way the doctrine under EU competition law, stressing the main differences with the US and the principal controversies raised by its application in Europe. The author concludes by addressing the question of the necessity and legitimacy of the doctrine under both legal systems.