Book excerpt: This study focuses on a rapidly developing, but still highly controversial, area of EU law: the emergence of general principles with constitutional relevance for EU civil law guiding its interpretation, gap filling, and legality control. The book brings to light seven principles in the case law of the Court of Justice of the European Union and in the Charter of Fundamental Rights. Principles 1, 2, and 3 on framed autonomy, protection of the weaker party, and non-discrimination are now part of substantive EU law, mainly contract law. Principle 4 on effectiveness, together with the principle of equivalence, is an "old acquaintance" of EU law and has mostly to do with procedures, but can also be extended to cover substantive and remedial matters. Principles 5 and 6 on balancing and proportionality are primarily concerned with methodological questions: the first has to do with judicial interpretation and application of EU civil law, the second with legal-political questions on the future of a (questionable) codified or optional EU civil law, in particular sales law. Finally, Principle 7 on good faith is still an emerging principle, but is gradually gaining importance. This book will allow the reader to understand and to assess the current evolution of EU civil law, in days where its autonomous character is increasingly recognized in the case law of the Court, and where the Charter is having a growing impact on its constitutional foundations.