Margaret Crosby "Peggy" Rathmann (born March 4, 1953) is an American writer and illustrator best known for children's picture books.
She was born in St. Paul, Minnesota, and graduated from the University of Minnesota. Her first book, Ruby the Copycat, earned Ms. Rathmann the "Most Promising New Author" distinction in Publishers Weekly's 1991 annual Cuffie Awards. That book was followed by her illustrations of Barbara Bottner's Bootsie Barker Bites, Good Night Gorilla about Peggy's experiences with gorillas, and Rathmann's Caldecott Medal winning Officer Buckle and Gloria. Since that book, Rathmann has written two more: Ten Minutes till Bedtime and The Day The Babies Crawled Away (which made it onto the Horn Book Fanfare List for the best books of 2003).
Rathmann lives in Nicasio, California.