Chapter 2 identifies a significant principle, immanent in tort law, vindicating the value in cooperative human arrangements. ‘Tort’s cooperation principle’ illuminates the necessity, at the duty of care stage in negligence claims, of analysing the prior dealings of the relevant parties. In claims between participants to a commercial arrangement, tort’s support for cooperation manifests in a preference for protecting the security of the coming together of the parties by refusing to recognise entitlements that would circumvent the arrangement. The common judicial assessment that society and the market expect commercial parties to be economically self-reliant exposes the importance of interrogating the reasonableness of commercial claimants’ reliance, for their own economic protection, on fellow participants in a commercial arrangement. This perspective reveals a long-standing doctrinal discontinuity and calls into question the reasoning used to support the Hedley Byrne & Co. Ltd. v. Heller & Partners Ltd. line of authority in commercial disputes.