This monograph, which was also designed as a short reference book for specialized undergraduate and graduate courses on EU law, intends to shed light on, and legally frame, the evolution of the doctrine of services of general economic interest (SGEIs). The book emphasizes the pivotal role played by SGEIs in striking a fair balance between market and social objectives. To this end, the book claims, first of all, that SGEIs have a dual nature inasmuch as they act as a limitation to/derogation from the free market and, simultaneously, as a value and positive obligation addressed at national authorities, undertakings, and EU institutions. The EU notions of access to public services and universal service are the clearest signal of such phenomenon. Secondly, the book claims that the transfer of competences from the Union to the Member States and the reaffirmation of Member States' sovereignty in crucial sectors of the economy are not the only solutions to foster social rights. In fact, this narrative is apt to undermine the foundations, spirit, and purpose of the process of European integration, especially at a time like the present, when new forms of populism and anti-Europeanism are on the rise, and when a European response is imperative to counter the spread of the coronavirus in European countries. The book concludes that SGEIs' regulation is an area of law where the EU institutions have generally successfully put into action and consolidated the social market economy principles on which the EU was founded. This is even further proof that the EU is not merely the reflection of interests linked to market completion, but also and foremost a 'Community based on the rule of law'.The book will be a valuable resource for academics and researchers in EU Law, European Public Law and EU competition law.