This chapter analyses the process of rule-making in the maritime transport industry. It uses the term ‘spontaneous law’ to refer to norms that emerge as a result of regular and repeated interactions among participants in shipping networks, interactions that create common understandings as to how contractual obligations undertaken are to be performed. The rule-making activity results in a combination of articulated or expressed rules that are enforceable directly as a result of the formation of a valid and binding contract; and unexpressed (or implicit) understandings that form part of the contractual context and that supplement the expressed rules. The context within which these unarticulated rules come into existence is a commercial network of contractual relationships. The chapter engages with the pragmatic question of how and to what extent these unarticulated rules will be enforced by the courts in the resolution of a dispute, focusing on the courts of England and Wales.