This chapter examines the evolution of Iron Age societies in north-west Europe. In recent decades, vast numbers of rural sites have been excavated across north-west Europe, complementing longstanding research on fortified sites and cemeteries. As would be expected of highly interconnected societies, continental and insular developments were broadly in step throughout the period, but regional diversity is apparent in settlement architecture and mortuary and ritual practices. Underpinned by an increasingly reliable agricultural base, population rose dramatically during the period in most regions, and many hitherto little-exploited areas of landscape were opened up to settlement. Craftworking became more specialized and new types of central foci emerged, often with important economic or cult functions, and sometimes reaching monumental proportions. After 125 BC, Roman intervention impacted progressively on north-west Europe, promoting ethnogenesis and other changes; the final section considers the Roman Iron Age in areas that remained outside the Empire.