A paperback is a type of book characterized by a thick paper or paperboard cover, and often held together with glue rather than stitches or staples. In contrast, hardcover or hardback books are bound with cardboard covered with cloth. The pages on the inside are made of paper.
Inexpensive books bound in paper have existed since at least the 19th century in such forms as pamphlets, yellowbacks, dime novels, and airport novels. Modern paperbacks can be differentiated by size. In the U.S., there are "mass-market paperbacks" and larger, more durable "trade paperbacks." In the U.K., there are A-format, B-format, and the largest C-format sizes.
Paperback editions of books are issued when a publisher decides to release a book in a low-cost format. Cheaper, lower quality paper; glued (rather than stapled or sewn) bindings; and the lack of a hard cover may contribute to the lower cost of paperbacks. Paperbacks can be the preferred medium when a book is not expected to be a major seller or where the publisher wishes to release a book without putting forth a large investment. Examples include many novels, and newer editions or reprintings of older books.
Since paperbacks tend to have a larger profit margin, many publishers try to balance the profit to be made by selling fewer hardcovers against the potential profit to be made by selling more paperbacks with a smaller profit per unit. First editions of many modern books, especially genre fiction, are issued in paperback. Best-selling books, on the other hand, may maintain sales in hardcover for an extended period to reap the greater profits that the hardcovers provide.
The early 19th century saw numerous improvements in the printing, publishing and book-distribution processes, with the introduction of steam-powered printing presses, pulp mills, automatic type setting, and a network of railways. These innovations enabled the likes of Simms and McIntyre of Belfast,Routledge & Sons (founded in 1836) and Ward & Lock (founded in 1854) to mass-produce cheap uniform yellowback or paperback editions of existing works, and distribute and sell them across the British Isles, principally via the ubiquitous W H Smith & Sons newsagent found at most urban British railway stations. These paper bound volumes were offered for sale at a fraction of the historic cost of a book, and were of a smaller format (110x175mm) aimed at the railway traveller. The Routledge's Railway Library series of paperbacks remained in print until 1898, and offered the traveling public 1,277 unique titles.
The German-language market also supported examples of cheap paper-bound books: Bernhard Tauchnitz started the Collection of British and American Authors in 1841. These inexpensive, paperbound editions, a direct precursor to mass-market paperbacks, eventually ran to over 5,000 volumes. Reclam published Shakespeare in this format from October 1857 and went on to pioneer the mass-market paper-bound Universal-Bibliothek series from 10 November 1867.
The German publisher Albatross Books revised the 20th-century mass-market paperback format in 1931, but the approach of World War II cut the experiment short. It proved an immediate financial success in the United Kingdom in 1935 when Penguin Books adopted many of Albatross' innovations, including a conspicuous logo and color-coded covers for different genres. British publisher Allen Lane invested his own financial capital to launch the Penguin Books imprint in 1935, initiating the paperback revolution in the English-language book-market by releasing ten reprint titles. The first released book on Penguin's 1935 list was André Maurois' Ariel.
Lane intended to produce inexpensive books. He purchased paperback rights from publishers, ordered large print runs (such as 20,000 copies--large for the time) to keep unit prices low, and looked to non-traditional book-selling retail locations. Booksellers were initially reluctant to buy his books, but when Woolworths placed a large order, the books sold extremely well. After that initial success, booksellers showed more willingness to stock paperbacks, and the name "Penguin" became closely associated with the word "paperback".
In 1939, Robert de Graaf issued a similar line in the United States, partnering with Simon & Schuster to create the Pocket Books label. The term "pocket book" became synonymous with paperback in English-speaking North America. In French, the term livre de poche was used and is still in use today. De Graaf, like Lane, negotiated paperback rights from other publishers, and produced many runs. His practices contrasted with those of Lane by his adoption of illustrated covers aimed at the North American market. To reach an even broader market than Lane, he used distribution networks of newspapers and magazines, which had a lengthy history of being aimed (in format and distribution) at mass audiences. This was the beginning of mass-market paperbacks.
Because of its number-one position in what became a very long list of pocket editions, James Hilton's Lost Horizon is often cited as the first American paperback book. However, the first mass-market, pocket-sized, paperback book printed in the US was an edition of Pearl Buck's The Good Earth, produced by Pocket Books as a proof-of-concept in late 1938, and sold in New York City. It has since become very collectible.
Through the circulation of the paperback in kiosks and bookstores, scientific and intellectual knowledge was able to reach the masses. This occurred at the same time that the masses were starting to attend university, leading to the student revolts of 1968 prompting open access to knowledge. The paperback book meant that more people were able to openly and easily access knowledge and this led to people wanting more and more of it. This accessibility posed a threat to the wealthy by imposing that it would be turned upside down, as the masses were now able to access almost all of the knowledge the wealthy previously had access to. Treating the paperback as any other book drastically weakened the distinction between high and low culture. The paperback revolution essentially broke this relationship by redefining it through access to knowledge.
In the United States, many companies entered the paperback publishing field in the years after Pocket Books' inception, including Ace, Dell, Bantam, Avon and dozens of other smaller publishers. At first, paperbacks consisted entirely of reprints, but in 1950, Fawcett Publications' Gold Medal Books began publishing original works in paperback.
Fawcett was also an independent newsstand distributor, and in 1945, the company negotiated a contract with New American Library to distribute their Mentor and Signet titles. That contract prohibited Fawcett from becoming a competitor by publishing their own paperback reprints. Roscoe Kent Fawcett wanted to establish a line of Fawcett paperbacks, and he felt original works would not be a violation of the contract. To challenge the contract, Fawcett published two anthologies--The Best of True Magazine and What Today's Woman Should Know About Marriage and Sex--reprinting material from Fawcett magazines not previously published in books. When these books were successfully published, he announced Gold Medal Books, a line of paperback originals. Sales soared, prompting Gold Medal editorial director Ralph Daigh to comment, "In the past six months we have produced 9,020,645 books, and people seem to like them very well." However, hardcover publishers resented Roscoe Fawcett's innovation, as evidenced by Doubleday's LeBaron R. Barker, who claimed that paperback originals could "undermine the whole structure of publishing."
Genre categories began to emerge, and mass-market book covers reflected those categories. Mass-market paperbacks influenced slick and pulp magazines. The market for cheap magazines diminished when buyers began to buy cheap books instead. Authors also found themselves abandoning magazines and writing for the paperback market. The leading paperback publishers often hired experienced pulp magazine cover artists, including Rudolph Belarski and Earle K. Bergey, who helped create the look and feel of paperbacks and set an appealing visual standard that continues to this day. Scores of well-known authors were published in paperback, including Arthur Miller and John Steinbeck.
World War II brought both new technology and a wide readership of men and women now in the military or employed as shift workers; paperbacks were cheap, readily available, and easily carried. Furthermore, people found that restrictions on travel gave them time to read more paperbacks. Four-color printing and lamination developed for military maps made the paperback cover eye catching and kept ink from running as people handled the book. A revolving metal rack, designed to display a wide variety of paperbacks in a small space, found its way into drugstores, dimestores, and markets. Soldiers received millions of paperback books in Armed Services Editions.
U.S. paperbacks quickly entered the Canadian market. Canadian mass-market paperback initiatives in the 1940s included White Circle Books, a subsidiary of Collins (U.K.); it was fairly successful but was soon outstripped by the success of Harlequin which began in 1949 and, after a few years of publishing undistinguished novels, focused on the romance genre and became one of the world's largest publishers.
McClelland and Stewart entered the Canadian mass-market book trade in the early 1960s, with its "Canadian best seller library" series, at a time when Canadian literary culture was beginning to be popularized, and a call for a Canadian author identity was discussed by the Canadian people.
A mass-market paperback is a small, usually non-illustrated, inexpensive bookbinding format. This includes the U.K. A-format books of 110 mm × 178 mm (4.3 in × 7.0 in) and the U.S. "pocketbook" format books of a similar size. These are generally printed on low quality paper, which discolors and disintegrates over a period of decades. They are commonly released after the hardback edition and often sold in non-traditional bookselling locations such as airports, drugstores, and supermarkets, as well as in traditional bookstores.
In 1982, romance novels accounted for at least 25% of all paperback sales. In 2013, 51% of paperback sales were romance. Many titles, especially in genre fiction, have their first editions in paperback and never receive a hardcover printing. This is particularly true of first novels by new authors.
Business practices by publishers and booksellers also differentiate mass-market paperbacks from hardbacks. When booksellers note that particular books are not selling, they may return them to the publisher for a refund or credit on future orders. However, in the case of mass-market paperbacks, this return usually means stripping the front cover, and returning only the cover for credit, while the remainder of the book is "pulped" (recycled). The copyright page often carries a warning that anyone who buys a book missing its front cover should assume that the publisher has received no payment and the author has received no royalties for that copy.
The mass-market paperbacks sold in airport newsstands have given rise to the vaguely defined literary genre of the "airport novel", bought by travelers to read during their potentially long hours of sitting and waiting. Mass-market paperbacks also have offered collections of comic strips and magazine cartoon series, such as Ernie Bushmiller's Nancy and Chon Day's Brother Sebastian.
The term B-format indicates a medium-sized paperback of 129 mm × 198 mm (5.1 in × 7.8 in). This size has been used to distinguish literary novels from genre fiction. In the U.S., books of this size are thought of as smaller trade paperbacks (see below).
A trade paperback, sometimes referred to as a "trade paper edition" or just "trades", is a higher-quality paperback book. If it is a softcover edition of a previous hardcover edition, and if published by the same publishing house as the hardcover, the text pages are normally identical to the text pages in the hardcover edition, and the book is close to the same size as the hardcover edition. Significantly, the pagination is the same so that references to the text will be unchanged: this is particularly important for reviewers and scholars. The only difference is the soft binding; the paper is usually of higher quality than that of a mass-market paperback, for example acid-free paper.
Trade paperbacks are typically priced lower than hardcover books and higher than mass-market paperbacks. Virtually all advance copies sent for promotional and review purposes are issued in trade paperback format.
In the U.S., the term trade paperback also encompasses the medium-sized paperbacks described as B-format, above. Trade paperbacks are 135mm x 216mm. 
Trade paperbacks are often used to reprint several issues of a comic series in one volume, usually an important storyline or the entire series itself, and the name "trade paperback" has become synonymous with a collection of reprinted material. Graphic novels may also be printed in trade paperback form. Publishers sometimes release popular collections first in a hardback form, followed by a trade paperback months later. Examples include Marvel Comics' Secret War and DC Comics' Watchmen among many others.
Anton Philipp Reclam (1807-1896) fit paraître à partir d'octobre 1857 les OEeuvres complètes de Shakespeare au prix de vente de 1 Thaler et demi pour l'édition brochée at illustrée en douze volumes. [Anton Philipp Reclam (1807-1896) published from October 1857 the Complete Works of Shakespeare at a retail price of one and a half Thalers for the paper-bound and illustrated edition in twelve volumes]
[...] in 1867, with the coming into force of the constitution of the Northern German Federation [...], works by German authors deceased for 30 years or more officially became public domain. Entire libraries of very cheap paperback editions of German classics immediately flooded the market. And so Reclam, too, extended his paperback idea with the new series 'Universal-Bibliothek' (Universal Library') [...]. Thousands of titles eventually followed, which included nearly all the world's great literature. In this way, and despite most Western countries' imitations, Reclam paperbacks became the world's foremost paperback series.
Mother of Demons was published in September 1997, and it was only published in a mass-market paperback edition, as was the standard practice at the time for first novels.