A merger clause (often called an entire agreement or integration clause) states that the written contract is the complete and exclusive record of the parties’ bargain and supersedes prior drafts, negotiations, heads of terms and representations. It is a descriptive contractual device rather than a defined statutory term; its effect is shaped by case law. Key features typically include: an “entire agreement” statement, a supersession provision, and sometimes non-reliance wording aimed at pre-contractual statements. It is used across commercial, finance, construction and M&A contracts to manage parol evidence risk, limit collateral warranties and allocate responsibility for pre-contract communications.Enforceability is contextual. Fraud cannot be excluded. In England & Wales and Northern Ireland, clauses that exclude or limit liability for misrepresentation (including through non-reliance language) are subject to statutory reasonableness tests and consumer protections; similar scrutiny applies under unfair terms and consumer law generally. In Scotland, effectiveness is assessed under Scots contract law and the Unfair Contract Terms Act 1977; courts closely examine clarity, reasonableness and collateral undertakings. In Ireland, entire agreement clauses are recognised at common law; their ability to restrict reliance on pre-contract statements depends on construction and Irish unfair terms and consumer legislation.Distinct from the property doctrine of merger on completion; parties may expressly preserve collateral obligations.