A poster is any piece of printed or painted art or design to be attached to a wall or vertical surface. Typically posters include both textual and graphic elements, although a poster may be either wholly graphical or wholly text. Posters are designed to be both eye-catching and informative. Posters may be used for many purposes. They are a frequent tool of advertisers (particularly of events, musicians and films),propagandist, protestors and other groups trying to communicate a message. Posters are also used for reproductions of artwork,  particularly famous works, and are generally low-cost compared to original artwork. Posters are also a great canvas for street artist and muralist.

According to French historian max Gallo, "for over two hundred years, posters have been displayed in public places all over the world. Visually striking, they have been designed to attract the attention of passers-by, making us aware of a political viewpoint, enticing us to attend specific events, or encouraging us to purchase a particular product or service." The modern poster, as we know it, however, dates back to 1870 when the printing industry perfected color lithography and made mass production possible.

"In little more than a hundred years," writes poster expert John Barnicoat, "it has come to be recognized as a vital art form, attracting artists at every level, from painters like Toulouse-Lautrec and Mucha to theatrical and commercial designers."They have ranged in styles from Art Nouveau, Symbolism, Cubism, and Art Deco to the more formal Bauhaus and the often incoherent hippie posters of the 1960's.

By the 1890's, the technique had spread throughout Europe. A number of noted artists created poster art in this period, foremost amongst them Toulouse-Lautrec and Jules Cheret. Chéret is considered to be the "father" of advertisement placards. He was a pencil artist and a scene decorator, who founded a small lithography office in Paris in 1866. He used striking characters, contrast and bright colors, and created over 1000 advertisements, primarily for exhibitions, theatres, and products. The industry soon attracted the service of many aspiring painters who needed a source of revenue to support themselves.

Cheret developed a new lithographic  technique that suited better the needs of advertisers: he added a lot more color which, in conjunction with innovative typography , rendered the poster much more expressive. Not surprisingly, Chéret is said to have introduced sex in advertising or, at least, to have exploited the feminine image as an advertising ploy. In contrast with those previously painted by Toulouse-Lautrec , Chéret's laughing and provocative feminine figures meant a new conception of art as being of service to advertising.

Posters soon transformed the thoroughfares of Paris into the "art galleries of the street." Their commercial success was such that some of the artists were in great demand and theatre stars personally selected their own favorite artist to do the poster for an upcoming performance. The popularity of poster art was such that in 1884 a major exhibition was held in Paris.

By the 1890's, poster art had widespread usage in other parts of Europe, advertising everything from bicycles to bullfights. By the end of the 19th century, during an era known as the Belle Epoque the standing of the poster as a serious artform was raised even further. Between 1895 and 1900, Jules Chéret created the Masters of the Poster series that became not only a commercial success, but is now seen as an important historical publication. Alphonse Mucha and Eugene Grassef were also influential poster designers of this generation, known for their Art Nouveau  style and stylized figures, particularly of women. Advertisement posters became a special type of graphic art in the modern age. Poster artists such as Treophile, Albert Guillaume Henri Thiriet and others became important figures of their day, their art form transferred to magazines for advertising as well as for social and political commentary.

In the United States, posters did not evolve to the same artistic level. American posters were primarily directed towards basic commercial needs to deliver a written message. However, the advent of the travelling circus brought colorful posters to tell citizens that a carnival was coming to town. But these too were very commercially utilitarian, of average quality, and few saw any real artistic creativity.

Many posters have had great artistic merit  and have become extremely collectible. These include the posters advertising Worlds Fair and Colonial Exhibitions.Other times of great turmoil also produced great posters. The 1960s with the rise of Pop Art and protest movements throughout the West; both made great use of posters. Perhaps the most acclaimed posters were those produced by French students during the so-called "événements" of May 1968. During the 1969 Paris Students Riot and for years to come, Jim Fitzpatric stylized poster of Marxist revolutionary Che Guevara (based on the photo Guerrillero Heroico), also became a common youthful symbol of rebellion.

Another example of 1st Amendment Rights is "The Four Freedoms",  a series of Art Posters by American Artist Norman Rockwell. The posters represent American's Freedom of Speech, Freedom of Worship, Freedom From Want and Freedom From Fear. At one time they were commonly displayed in post offices, schools, clubs, and on a variety of public and private buildings

The film industry quickly discovered that vibrantly colored posters were an easy way to sell their pictures. Today, posters are produced for most major films, and the collecting of movie posters has become a major hobby. The record price for a poster was set on November 15, 2005 when US$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 tremendous prices as well, with an example from The Mummy realizing $452,000 in a 1997  Sotheby's auction, and posters from both The Black Cat and Bride of Frankenstein selling for $334,600 in various Heritage Auctions. The 1931 Frankenstein 6-sheet poster, of which only 1 copy is known to exist, is considered to be the most valuable film poster in the world.

Posters advertising events have become common. Any sort of public event, from a rally to a play, may be advertised with posters; a few types of events have become notable for their poster advertisements.

Many concerts, particularly rock concerts, have custom-designed posters that are used for advertisement of the event. These often become collectors items as well.

Posters that showcase the people's favorite artist, movie, play, car, products, or music group are popular in teenagers' bedrooms, college dorm rooms, homes, businesses, buildings and city streets. Today, companies like Sky Posters are a creative service and a creative seller of great Pop Art & Commercial Posters and a producer of large poster images for business, public service groups and the public.