The book engages in the debate about the so-called ‘lex mercatoria’ by offering a theoretically justified and pragmatic account. It tests the proposition that the lex mercatoria is a universal, a-national, autonomous legal system developed spontaneously by merchants. The book evaluates the existing explanations of the lex mercatoria and argues that the most promising account considers it to consist solely of unwritten trade usage. The book extends the discussion of the topic to public international law and jurisprudence. It draws parallels with customary international law and examines the circ ... More

The book engages in the debate about the so-called ‘lex mercatoria’ by offering a theoretically justified and pragmatic account. It tests the proposition that the lex mercatoria is a universal, a-national, autonomous legal system developed spontaneously by merchants. The book evaluates the existing explanations of the lex mercatoria and argues that the most promising account considers it to consist solely of unwritten trade usage. The book extends the discussion of the topic to public international law and jurisprudence. It draws parallels with customary international law and examines the circularity paradox of opinio juris. The book considers the notion of social rules and evaluates the function of primary and secondary rules within a legal system to explain how normative practices develop within a business community and become rules of ‘a-national law’. After the theoretical clarification, the book offers a pragmatic model which adopts a ‘two-element’ approach to the lex mercatoria. It argues that a lex mercatoria rule emerges when (i) congruent majority conduct is followed out of a (ii) critical reflective attitude by the majority within a business community. Based on this model, the book discusses conflict of laws issues and makes proposals on how parties and arbitrators may select the lex mercatoria as the governing law with greater certainty. The book examines the evidentiary process of how these two elements may be proved in arbitration or in court proceedings where a trade usage must be established and considers the documentary and witness evidence available to prove a lex mercatoria rule.