Anglo-Norman is the name traditionally given to the dialect of Medieval French imported into Britain in the wake of the Norman Conquest of 1066. From its beginnings as an everyday vernacular, it rapidly developed into a written language of record, instruction and literature, serving the needs of the French-speaking élite which formed the governing and socially dominant class of Britain during the 12th and 13th centuries. Despite the rapid assimilation of the Normans and their descendants into British society, their language persisted well beyond its natural lifespan into the 14th century and beyond. The most tangible and durable legacy of Anglo-Norman lies in its enrichment of the English language, particularly its vocabulary, but it has also left behind it a wide and varied corpus of literary and other texts.
A more detailed introduction to Anglo-Norman is available via the introductory pages to the online Anglo-Norman Dictionary.