King John of England’s defeat by the French in 1204 led to the territorial fragmentation of the Duchy of Normandy. Henceforth, the Norman mainland, allied to France, and the Channel Islands, allied to England, would find themselves on different sides of an ever-widening linguistic gulf. In Variation and Change in Mainland and Insular Norman, Mari C. Jones examines the way in which contact between the Norman dialect and its two typologically different superstrates (French and English) provides optimal conditions to study the linguistic mechanisms of ‘dialect contact’ and ‘language contact’. Through the analysis of extensive and original phonological, morphosyntactic and lexical data, set in their historical and sociolinguistic contexts, this fascinating study explores how advergence with its superstrates has led Norman to diverge linguistically within these territories.