Lost Horizon is a 1933 novel by English writer James Hilton. The book was turned into a movie in 1937 by director Frank Capra of the same title. It is best remembered as the origin of Shangri-La, a fictional utopian lamasery high in the mountains of Tibet.

The book, published in 1933, caught the notice of the public only after Hilton's Goodbye, Mr. Chips was published in 1934. Lost Horizon subsequently became a huge popular success and in 1939 was published in paperback form, as Pocket Book #1. Because of its number-one position in what became a very long list of pocket editions, Lost Horizon is often mistakenly called the first American paperback book when in fact paperbacks had been around since the mid-1800s. What made Pocket Books #1 of revolutionary importance was that it had the distinction of being the very first "mass-market" paperback; "mass-market" paperbacks allowed people of modest means not just to own books they otherwise might not have been able to afford, it also made it possible for them to slip the paperback into their pocket for casual reading on the go, hence the name "Pocket Book." By the 1960s, Pocket Books alone, over the course of more than forty printings, had sold several million copies of "Lost Horizon" helping to make it one of the best-loved and most enduring novels of the 20th Century.

U.S. President Franklin D. Roosevelt named the Presidential hideaway in Maryland after Shangri-La. (It has since been renamed Camp David.) Likewise Roosevelt initially claimed the Doolittle Raid came from Shangri-La; this later inspired the name of the aircraft carrier USS Shangri-La.

The Shangri-La Hotels, based in Singapore but extending to Australia, Malaysia and other Asian countries, are also named and to some extent themed after the lamasery of the book. Some of the hotels provide guests with a complimentary copy of the book, a practice stretching back to the chain's first hotel in Singapore in the 1970s.