The architectural style is a classification of a building's appearance and also of its placement in the history of design. In order to belong to a particular style, a building usually has to have been designed during the period when that style was current; exceptions are sometimes made for very close facsimiles, but generally a construction using a long-outdated style is considered to belong to a revival style.

Each structure can be assigned only one style. When a building is a mixture of different styles, it is classified by the style which dominates its overall appearance. The exterior has priority over the interior in determining the dominant style.