Kathryn Margaret Rudy (born 25 February 1969) is a manuscript historian at the University of St Andrews, Scotland. She is best known for her forensic approach to medieval books, and has pioneered the use of the densitometer to measure the grime that original readers deposited in their books. Her research focuses on the medieval reception of manuscripts, how they were manipulated and handled, and how book-making skills were lost with the advent of the printing industry.