Originally, contract law was considered to be immune from the effect of fundamental rights, the function of which was limited to being individual defences against the vigilant eye of the state. This traditional view, however, has recently been put under pressure as a result of fundamental rights increasingly becoming relevant for contract law. In the first place, this book discusses the relationship between fundamental rights and private law in general in Germany, the Netherlands and the UK, as well as in EU law and the law of the ECHR, against the background of the underlying rationale for the distinction between public and private law as it has developed on the continent. Secondly, the book examines whether and, if so, how the interests of the weaker party can be protected on the level of fundamental rights, and contract law. The final part of this book builds upon the insights and conclusions drawn from the theoretical and practical perspectives to develop recommendations regarding the desirable extent of the constitutionalisation of contract law.