One of the remarkable things about international law is that it is often made by private organisations or conferences or institutes, who publish restatements, or model codes, or principles, and then promote the use of those by nations. If sufficient nations take them up, they become incorporated into the body of international law as examples of what is called soft law.
The International Institute for the Unification of Private Law, or UNIDROIT, has now developed three versions of its Principles of International Commercial Contracts, which are essentially a full code of law for international contracts.
provide a comprehensive law of contracts which does not belong to any individual country, but instead reflects what we might describe as being the general practice of nations in relation to contract law. The idea is that contracting parties, instead of agreeing that their contract will be bound by the law of any particular nation, might instead agree that their contract will be bound by the general laws of contract, as expressed by UNIDROIT.
The High Court of Australia has never decided a contract on the basis of the UNIDROIT principles. Neither has the Queensland Supreme Court.