EU law covers numerous sectors of private law and is still expanding. Due to its fragmentary nature, most legal literature addresses specific areas such as EU labour law, EU company law, EU private international law, EU consumer law, etc. In contrast, this book presents an innovative approach in its analysis of EU private law, considering its continuous expansion as an ongoing process and interrogating some central questions: What is private law in the framework of the EU? How does EU private law relate to traditional concepts of private law? What is the impact on horizontal relations of the law of the Union which was established with a view to the integration of peoples in Europe? Is the frequent reference to the policy orientation of EU law sufficient to overcome the differences between public and private law? Like the growth rings of a tree the numerous acts and judgments of EU private law feed from the trunk and the roots, which developed in the vertical relations between the Union and the Member States. The foundations of EU law, which often have a background in legal history, comparative experience and public international law, impact upon horizontal relations in a manner previously unknown in national systems of private law. Across ten parts grouped in four books devoted to foundations, principles, enforcement and implementation, respectively, as well as the external dimension, the author elaborates on the peculiarities of EU private law as compared to the traditional analysis of private law in any given national legal system. The author traces throughout the book the origins of legal principles and rules in comparative law, legal history and public international law and their application and development in EU private law instruments and the judgments of the CJEU. This comparison helps to strengthen our understanding of those peculiarities and paves the way for a comprehensive critical assessment of the state of EU private law today.