In 1845 a master of English commercial law wrote that there was ‘no part of the history of English law more obscure than that connected with the maxim that the law merchant is part of the law of the land’. Since then there have been detailed studies of the medieval law merchant and of the later development of English mercantile law, but the precise status of the law merchant in England, and the nature of the process by which it supposedly became fused with the common law, remain as obscure as they were in 1845. The obscurity begins with the very concept of the ‘law merchant’, which has been differently understood by different writers and continues to be used in widely divergent senses. Some have regarded it as a distinct and independent system of legal doctrine, akin in status to Civil or canon law, and perhaps derived from Roman law. Others have supposed it to be a particular aspect of natural law, or the universal jus gentium, and as such akin to international law. Another school regards it as a form of immemorial custom, which by familiarity was eventually noticed by the common-law judges in the same way as the customs of gavelkind and borough English were judicially noticed, without formal proof. Yet a fourth view, which was doubtless influenced by the seventeenth-century writer Malynes, is that the law merchant is the same thing as mercantile practice, the changeable usages of merchants.