A commemorative plaque, or simply plaque, or in other places referred to as a historical marker, historic marker, or historic plaque, is a plate of metal, ceramic, stone, wood, or other material, bearing text or an image in relief, or both, to commemorate one or more persons, an event, a former use of the place, or some other thing. Most such plaques are attached to a wall, stone, or other vertical surface.

Many modern plaques and markers are used to associate the location where the plaque or marker is installed with the person, event, or item commemorated as a place worthy of visit. A monumental plaque or tablet commemorating a deceased person or persons, can be a simple form of church monument. Most modern plaques affixed in this way are commemorative of something, but not all. There are also purely religious plaques, and some signify ownership or affiliation of some sort. A plaquette is a small plaque, but in English, unlike many European languages, the term is not typically used for outdoor plaques fixed to walls.

The Benin Empire, which flourished in present-day Nigeria between the thirteenth and nineteenth centuries, had an exceedingly rich sculptural tradition. One of the kingdom's chief sites of cultural production was the elaborate ceremonial court of the Oba (divine king) at the palace in Benin. Among the wide range of artistic forms produced at the court were rectangular brass or bronze plaques. At least a portion of these plaques, which were mainly created from the thirteenth through sixteenth centuries, commemorate significant persons and events associated with the Oba's court, including important battles during Benin's sixteenth century expansionary period.

Brass or bronze memorial plaques were produced throughout medieval Europe from at least the early thirteenth through the sixteenth centuries as a form of sepulchral memorial generally inset into the walls of churches or surfaces of tombs. Surviving in great numbers, they were manufactured from sheet brass or latten, very occasionally coloured with enamels, and tend to depict highly conventional figures with brief inscriptions.

Historical markers are put on display by the owners of sites listed by national agencies concerned with historic preservation such as the National Trust for Historic Preservation and the National Register of Historic Places (in the United States), the National Trust for Places of Historic Interest or Natural Beauty (in the United Kingdom), An Taisce (in Ireland), National Historical Commission of the Philippines (in the Philippines), and the National Trusts of other countries.

Other historical markers are created by local municipalities, non-profit organizations, companies, or individuals. In addition to geographically defined regions, individual organizations, such as E Clampus Vitus or the American Society of Mechanical Engineers, can choose to maintain a national set of historical markers that fit a certain theme.

The Royal Society of Arts established the first scheme in the world for historical commemoration on plaques in 1866.

The scheme was established under the influence of the British politician William Ewart and the civil servant Henry Cole. The first plaque was unveiled in 1867 to commemorate Lord Byron at his birthplace, 24 Holles Street, Cavendish Square. The earliest historical marker to survive, commemorates Napoleon III in King Street, St James's, and was also put up in 1867.