The ‘law merchant’ is said to be a part of the law of England, and this proposition is acknowledged in our statute law, though few if any modern commentators have thought its meaning worth exploration. Moreover, although less is heard of the law merchant nowadays than in the nineteenth century, the expression has occasionally surfaced in recent cases – or at any rate in what middle-aged lawyers think of as recent cases. Most of these recent references, when not simply quoting from nineteenth-century judgments, are effectively historical statements purporting to explain the source of some rule of common or statute law. In other passages, the term is used rather loosely as a synonym for mercantile or commercial law. It might be deduced from these citations that the law merchant belongs more to the world of legal history than to that of the commercial courts of the twenty-first century. There is certainly a strong case for leaving it there. On the other hand, it has been said on high authority that the ‘mediaeval law merchant’ is still available as a source when required, while in other jurisdictions the lex mercatorum of the early-modern jurists has enjoyed a modest renaissance. At any rate, the law merchant has a sufficient toehold in the real world of today to justify the question whether it can properly be regarded as a vital source of legal ideas, as some kind of living entity which stimulates legal evolution in the commercial sphere, or whether it is really another example of Lord Mansfield's ‘well meaning sloppiness of thought’.