The interactions of the Celtic-speaking communities of Southern Gaul with the Mediterranean world have intrigued commentators since antiquity. This book combines sociolinguistics and archaeology to bring to life the multilingualism and multiple identities of the region from the foundation of the Greek colony of Massalia in 600 BC to the final phases of Roman Imperial power. It builds on the interest generated by the application of modern bilingualism theory to ancient evidence by modelling language contact and community dynamics, and adopting an innovative interdisciplinary approach. This produces insights into the entanglements and evolving configurations of a dynamic zone of cultural contact. Key foci of contact-induced change are exposed and new interpretations of cultural phenomena highlight complex origins and influences from the entire Mediterranean koine. Southern Gaul reveals itself to be fertile ground for considering the major themes of multilingualism, ethnolinguistic vitality, multiple identities, colonialism and Mediterraneanization.