Penguin Books demonstrated that large audiences existed for humorous books.
Only paperback editions were published until the King Penguin series debuted in 1939, and latterly the Pelican History of Art was undertaken; these works, considered unsuitable as paperbacks because of their lengths and copious illustrations on art paper, were cloth-bound
 In 1940, the children's imprint Puffin Books began with a series of non-fiction picture books; the first work of children's fiction published under the imprint was Barbara Euphan Todd's Worzel Gummidge the following year

