The late Middle Ages in England saw a flowering of scientific writing in the vernacular that moved English discourse in new directions and established new textual genres. This book examines the sociolinguistic causes and effects of that process, based on the empirical evidence from manuscripts and computerized files. Topics covered include scriptorial "house-styles", code-switching, translation strategies, and transmission processes. The book offers important new insights into vernacularization phenomena, and will be welcomed by historical linguists and medievalists alike.