The notion of mandatory rules originates, at least in civil-law systems, in domestic law, where they are contrasted with permissive or default rules; they are the rules which the EC Rome Convention defined as the ”rules of law which cannot be derogated from by contract.”1 In the context of conflict of laws, the concept of mandatory rules (lois de police) developed to denote the transnational application of a mandatory norm, based on legislative intent, irrespective of the designation of the applicable law through the mediation of a conflict rule. It follows from that description that the concept has limited meaning in those jurisdictions which routinely adopt a unilateral approach or methodology for conflict of laws, focusing on the content and purpose of the competing laws in order to determine their spatial reach. However, this is not so true in the field of contracts, with which we are mostly concerned. There, the widely recognized principle is that the applicable law is the law designated by the parties. Whatever the jurisdiction, a court will be called upon to assess whether the parties' choice offends one or more mandatory rules of a State to which the contract is connected, and thus to inquire into its spatial reach.