This book reinvigorates the debate about the place of substantive fairness in contract law. Its central argument is that it is time we recognised a general judicial power to relieve against highly unreasonable contracts. The book suggests that in fact the courts have been modifying such contracts for a long time both in equity and at common law, but that anomalies, inconsistencies and gaps remain, which make the recognition of a residual judicial power to modify contracts on this ground desirable; and it invokes the concept of unjust or disproportionate enrichment as a justification for judicial intervention.