. Printers and publishers continuously developed new strategies to sell their products. . In the 19th century periodicals, serialised novels, gave birth to a particular way of writing novels. . In 1920s popular works were sold in cheap series called the Shilling Series in England. . The dust cover or the book jacket is also a twentieth century innovation. . With the onset of Great Depression in the 1930s publishers feared a decline in book purchases. To sustain buying, they brought out cheap paperback editions.