Mary Eileen Chalmers (born March 16, 1927) is an American author and illustrator who has written children's books frequently featuring cats from the 1950s through the 1980s. She is known for her books about Harry, an anthropomorphic cat. Her books were well known for featuring her own illustrations in addition to the written text, including a unique complex layout with full pages of text and drawings woven throughout the pages and within the margins. She also provided illustrations for many other authors' books, especially those involving animals.