A poster is usually a printed paper announcement or advertisement that is exhibited publicly. Whether promoting a product, event, or sentiment (such as patriotism), a poster must immediately catch the attention of the passerby. There is no set way to accomplish this; success can stem, for example, from the instantaneous impact of a concise, striking design or from the sumptuous appeal of an ornate work of art.

By extension, the term poster is used to denote a paper panel printed for display as a novelty or as a work of art. Although printed public advertisements can be traced to the 15th century, the poster as it is understood today did not emerge until around 1860, given impetus by the invention of lithography, which allowed brilliantly colored posters to be produced cheaply and easily.

The first of the great modern poster artist, Jules Cheret, began his career in 1867 with a theatrical poster announcing a performance by Sarah Bernhardt. His captivating depiction's of the entertainers of Parisian nightlife, rendered in clear, radiant colors, dominated Paris displays for the last 30 years of the 19th century and also attracted others to the medium. The result was extraordinary diversity of style, from the folk art imagery of anonymous lithographers to major works by the best known of the poster artists.

Henri de Toulouse-Lautrec's posters of the 1890’s, characterized by bold, dramatic designs, are lively and sensitive depiction's of Parisian personalities. Interest in the poster was heightened by the appearance in the 1890s of the style known as Art Nouveau, characterized by flowing, organic lines, elegant grace, and a richly complex symbolism. Because it combined decorative brilliance with a faith that fine art could be popular and useful, the movement found the poster a natural form. The undisputed master of Art Nouveau was a Czech living in Paris, Alphonse Mucha. His first poster was for Sarah Bernhardt; its exotic Byzantine ornament and subtle use of color brought him overnight success; it was the first of a legacy of posters by him, ranging from grand theatre announcements to advertisements for cigarette papers and chocolate, that remain unsurpassed in beauty and inventiveness. Among the many other manifestations of the Art Nouveau poster were, in Paris, the elegant works of Georges de Feure and Eugene Grasset; in The Netherlands, the stylized posters of Jan Toorop; in Austria, the elegantly ordered works of Koloman Moser and Alfred Roller; and, finally, the work of Will Bradley, who brought the style to the United States.

With the outbreak of World War I in 1914, the poster became an art that could influence history. Prior to the ascendancy of motion pictures and television, it was politically the most important of all visual media. It was easily produced and immediate in impact, and it could be posted wherever there was a public to see it. Given such a role, posters of war and revolution may be quite forceful, varied, and revealing. The propagandistic posters of the early years of the Soviet Union, for example, aimed at a largely illiterate population, are blunt and powerful; those of the late Austro-Hungarian Empire have a lyrical medieval gallantry; and those of World War I America display a swaggering hometown naivete. All reveal a need to embody not only the aspirations of the group that produced them but of the entire people to whom they were addressed. An outstanding example is James Montgomery Flagg's famous U.S. recruiting poster of Uncle Sam pointing directly at the viewer, a forceful call to patriotism during World War I.

The industrial boom of the early 20th century gave rise to advertising posters for virtually every conceivable product and event. Many express the spirit or stylistic excess of their day, from the primitive and folk art quality of early circus posters to the sophisticated and streamlined travel posters of the 1930s.

The onslaught of radio and television and an almost complete reliance on photography in advertising, however, brought about an eclipse in poster art. From the 1960s on, a regeneration of popular art forms, beginning with popular music, led to a new interest in posters. In San Francisco, where the movement was strongest, posters announcing weekly dance hall concerts echoed the golden age of the poster of the 1890s.