Book excerpt: Vitiation of Contracts proposes a new theory to explain the rationale of general vitiating factors in English contract law. It provides a clear link to voluntariness as the foundation of contractual liability and compares the English position, in light of this theory, with the Principles of International Commercial Contracts (PICC), the Principles of European Contract Law (PECL), the Draft Common Frame of Reference (DCFR) and the US Restatement (Second) of Contracts.