The aim of this paper is to conciliate some conclusions of the economic theories of breach of contract and tort law. The main result is that the two efficient alternatives that tort law identifies (negligence rule and strict liability with a defense of contributory negligence) are mirrored by two efficient ways of defining contract damages. The first consists of forcing the debtor to pay expectation damages but limiting the level of the creditor’s reliance (rule of damage mitigation). The second consists of obliging the debtor to pay expectation damages only when his breach of contract implies negligence, otherwise using restitution remedies (doctrines of impracticability and force majeure)