A film poster is a poster used to promote and advertise a film primarily to persuade paying customers into a movie theater to see it. Studios often print several posters that vary in size and content for various domestic and international markets. They normally contain an image with text. Today's posters often feature printed likenesses of the main actors. Prior to the 1980s, illustrations instead of photos were far more common. The text on film posters usually contains the film title in large lettering and often the names of the main actors. It may also include a tagline, the name of the director, names of characters, the release date, and other pertinent details to inform prospective viewers about the film.

Film posters are often displayed inside and on the outside of movie theaters, and elsewhere on the street or in shops. The same images appear in the film exhibitor's pressbook and may also be used on websites, DVD (and historically VHS) packaging, flyers, advertisements in newspapers and magazines, and all other press related to the promotion of the film.

Film posters have been used since the earliest public exhibitions of film. They began as outside placards listing the programme of (short) films to be shown inside the hall or movie theater. By the early 1900s, they began to feature illustrations of a film scene or an array of overlaid images from several scenes. Other posters have used artistic interpretations of a scene or even the theme of the film, represented in a wide variety of artistic styles. Film posters have become increasingly coveted by art collectors in recent years due to their known relative rarity, condition, artist, and art historical significance.

The first poster for a specific film, rather than a "magic lantern show", was based on an illustration by Marcellin Auzolle to promote the showing of the Lumiere Brothers film L'Arroseur arrosé at the Grand Café in Paris on December 26, 1895.

Originally, film posters were produced for the exclusive use by the theaters exhibiting the film the poster was created for, and were required to be returned to the distributor after the film left the theater. In the United States, film posters were usually returned to a nationwide operation called the National Screen Service (NSS) which printed and distributed most of the film posters for the studios between 1940 and 1984. As an economy measure, the NSS regularly recycled posters that were returned, sending them back out to be used again at another theater. During this time, a film could stay in circulation for several years, and so many old film posters were badly worn before being retired into storage at an NSS warehouse (most often, they were thrown away when they were no longer needed or had become too worn to be used again). Those posters which were not returned were often thrown away by the theater owner or damaged by being outside.

Beginning in the 1980s, American film studios began taking over direct production and distribution of their posters from the National Screen Service and the process of making and distributing film posters became decentralized in that country. As Hollywood cinema was disseminated into foreign markets, distinct hand-painted film poster traditions arose in Poland, India, and Ghana, with depictions of posters often varying from their original Hollywood versions based on the artistry of local painters.

After the National Screen Service ceased most of its printing and distribution operations in 1985, some of the posters which they had stored in warehouses around the United States ended up in the hands of private collectors and dealers. Today there is a thriving collectibles market in film posters, and some have become very valuable. The first auction by a major auction house solely of film posters occurred on December 11, 1990, when proceeds of a sale of 271 vintage posters run by Bruce Hershenson at Christie's totaled US$935,000. The record price for a single poster was set on November 15, 2005, when $690,000 was paid for a poster of Fritz Lang's 1927 film Metropolis from the Reel Poster Gallery in London. Other early horror and science fiction posters are known to bring extremely high prices as well, with an example from The Mummy realizing $452,000 in a 1997 Sotheby's auction, and posters from both Bride of Frankenstein and The Black Cat selling for $334,600 in Heritage Auctions, in 2007 and 2009, respectively.

Occasionally, rare film posters have been found being used as insulation in attics and walls. In 2011, 33 film posters, including a Dracula Style F one-sheet (shown right), from 1930 to 1931 were discovered in an attic in Berwick, Pennsylvania and auctioned for $502,000 in March 2012 by Heritage Auctions.