A poster is a large sheet that is placed either on a public space to promote something or on a wall as decoration. 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, propagandists, 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 the original artwork. The modern poster, as we know it, however, dates back to the 1840s and 1850s when the printing industry perfected colour lithography and made mass production possible.

Chromolithography is a method for making multi-colour prints. This type of colour printing stemmed from the process of lithography, and includes all types of lithography that are printed in colour. When chromolithography is used to reproduce photographs, the term photochrome is frequently used. Lithography is a method of printing on flat surfaces using a flat printing plate instead of raised relief or recessed intaglio techniques.