Martin Waddell (born 10 April 1941) is an Irish writer of children's books. He may be known best for the texts of picture books that feature anthropomorphic animals, especially the Little Bear series illustrated by Barbara Firth (not to be confused with Minarik & Sendak's Little Bear series). He also writes under the pen name Catherine Sefton, for older children, primarily ghost stories and mystery fiction. The work by Sefton most widely held in WorldCat libraries is the novel In a blue velvet dress (1973).
For his "lasting contribution" as a children's writer Waddell received the Hans Christian Andersen Medal in 2004.