Source: Wikipedia, "Pocket Books", available under the CC-BY-SA License.
Pocket produced the first mass-market, pocket-sized paperback books in America in early 1939 and revolutionized the publishing industry. The German Albatross Books had pioneered the idea of a line of color-coded paperback editions in 1931 under Kurt Enoch; Penguin Books in Britain had refined the idea in 1935 and had 1 million books in print by the following year.
In 1944, the founding owners sold the company to Marshall Field III, owner of the Chicago Sun newspaper. Following his death, in 1957, Leon Shimkin, a Simon & Schuster partner, and James M. Jacobson bought Pocket Books. Simon & Schuster acquired Pocket in 1966.
Penguin's success inspired entrepreneur Robert de Graff, who partnered with publishers Simon & Schuster to bring it to the American market. Priced at 25 cents and featuring the logo of Gertrude the kangaroo (named after the artist's mother-in-law), Pocket Books' editorial policy of reprints of light literature, popular non-fiction, and mysteries was coordinated with its strategy of selling books outside the traditional distribution channels. The format size, and the fact that the books were glued rather than stitched, were cost-cutting innovations.