The study of law often starts with a dictionary. The beginning law student, asked to read cases and textbooks, is thrown into a sea of strange vocabulary. Unfamiliar words are everywhere, and so too are familiar words used in unfamiliar ways. It is no surprise, then, that most students are advised to invest in a dictionary, and to use it. As Karl Llewellyn put it in the classic The Bramble Bush: ‘You are outlanders in this country of the law. You do not know the speech. It must be learned. Like any other foreign tongue, it must be learned: by seeing words, by using them until they are familiar; meantime, by constant reference to the dictionary’.1 But it is not only the law student who needs a law dictionary. Law is a discipline, not of formulae or images, but of words. The practising lawyer, the academic jurist, the translator, and the judge all need dictionaries, and it is no surprise to find that dictionaries of legal terms are one of the oldest genres of legal literature. Nor is it surprising to find, as the chapter by Mathieu Devinat illustrates, that appellate judges at the highest level have resort to law dictionaries when faced with difficult questions of interpretation. It was Oliver Wendell Holmes, Jr., speaking for the Supreme Court of the United States, who expressed a view that perhaps every lexicographer would share: ‘A word is not a crystal, transparent and unchanging, it is the skin of a living thought and may vary greatly in color and content according to the circumstances and time in which it is used’.2