It investigates in a wide-ranging and systematic fashion a foundational but under-considered factor in the history and culture of the Vikings in England. The subject is important for late Anglo-Saxon and Viking Age history; for language and literature in the late Anglo-Saxon period; and for the history and development of the English language. The work's primary focus is on Anglo-Norse language contact, with a particular emphasis on the question of possible mutual intelligibility between speakers of the two languages; but since language contact is an emphatically sociolinguistic phenomenon, the work's methodology combines linguistic, literary and historical approaches, and draws for its evidence on texts in Old English, Old Norse and Anglo-Latin, and other forms of linguistic and onomastic material.