This book has advanced three central claims, each related to a different branch of private law. First, to achieve efficiency under negligence law, all foreseeable risks should be included when setting standards of care and awarding damages. Second, to achieve efficient contracts, the law should respond more to the promisee's incentives for cooperation and reliance. Third, the law should encourage unrequested benefits by making the beneficiaries compensate the benefactors more often, and by reducing the liability of injurers and breaching parties who externalize benefits. In support of these claims, the book has introduced novel principles such as total liability for excessive harm, anti-insurance, decreasing liability contracts, and the public goods theory of restitution. In conclusion, the book proposes three main legal reforms to improve private law in terms of promoting social welfare, such as removing misalignments in tort law or reducing the benefactor's liability for accidents.