There are many attempts to define the subject. As an initial matter, the concept is to be kept distinct from notions such as ‘international business law’ or ‘international economic law’. In the book whose authors are teaching a course so titled since the mid 1990s it is introduced as follows:
‘Transnational commercial law consists of that set of rules, from whatever source, which governs international commercial transactions and is common to a number of legal systems. Such commonality is derived from international instruments of various kinds, such as conventions and model laws, and from codification of international trade usage adopted by contract, as exemplified by the Uniform Customs and Practice for Documentary Credits published by the International Chamber of Commerce and the Model Arbitration Rules issued by the United Nations Commission and International Trade Law (UNICITRAL). Legislative guides of the kind published by UNICITRAL and UNIDROIT are also contributing to the process of harmonization at international level. So too are ‘soft law’ restatements, such as the UNIDROIT Principles of International Commercial Contracts, which though not binding are regularly resorted to by arbitral tribunals and influence the shaping of domestic legislation in developing as well as ‘developed’ countries. Underpinning these is the lex mercatoria, consisting of the unwritten customs and usages of merchants, and general principles of commercial law.’
Roy Goode/Herbert Kronke/Ewan McKendrick, Transnational Commercial Law – Texts, Cases, and Materials, Oxford University Press, Oxford, 1st edition 2007, 2nd edition 2015, p. lxv.