This book is about a radically new scientific concept, how it was developed and promulgated, and finally came to be generally accepted. The concept in question is the archaeological Three Age System, the fundamental division of the prehistoric past into successive Ages of Stone, Bronze, and Iron. This is the basic chronology that now underpins the archaeology of most of the Old World. To be sure, we may question (for example) whether the transition from the Neolithic to the Early Bronze Age really marks as great a social and cultural change as that from Middle to Late Bronze Age; or we may debate whether the Mesolithic should really be so named, or should be referred to as the Epi-Palaeolithic. But the fact that we can even argue in such terms demonstrates the all-pervasive strength of the fundamental Stone–Bronze–Iron classification. Terms like ‘Mesolithic’ or ‘Late Bronze Age’ may create their own problems, and the precise definitions of such periods and the nature of the transitions between them are often keenly contested; but the debates they engender operate within the parameters of the Three Age System as a whole, and thus act to reinforce it. No-one, after all, doubts that the Stone Age preceded the Bronze Age. But it was not always so. There is an archaeology even of the Three Age System itself. It was conceived in Denmark and southern Sweden; it was initially published there in the mid-1830s, and was fully accepted and operating in those countries in under a decade. Its acceptance in southern Scandinavia was remarkably rapid, and no serious assault was made there upon its fundamentals. The same cannot be said for its reception in the British Isles, however. Its acceptance and uptake here was variable and patchy, and some leading British and Irish scholars shunned it for forty years. This is something which is almost always overlooked in histories of archaeology, which instead place emphasis on the people who adopted the Three Age System. This is entirely understandable, but it has led to the people who rejected the Three Age System being almost entirely written out of the history of the archaeology of the British Isles.