An architectural style is a classification of buildings (and nonbuilding structures) based on a set of characteristics and features, including overall appearance, arrangement of the components, method of construction, building materials used, form, size, structural design, and regional character.

Architectural styles are frequently associated with a historical epoch (Renaissance style), geographical location (Italian Villa style), or an earlier architectural style (Neo-Gothic style), and are influenced by the corresponding broader artistic style and the "general human condition". Heinrich Wölfflin even declared an analogy between a building and a costume: an "architectural style reflects the attitude and the movement of people in the period concerned".

The 21st century construction uses a multitude of styles that are sometimes lumped together as a "contemporary architecture" based on the common trait of extreme reliance on computer-aided architectural design (cf. Parametricism).^{[citation needed]}

Folk architecture (also "vernacular architecture") is not a style, but an application of local customs to small-scale construction without clear identity of the builder.

The concept of architectural style is studied in the architectural history as one of the approaches ("style and period") that are used to organize the history of architecture (Leach lists five other approaches as "biography, geography and culture, type, technique, theme and analogy"). Style provides an additional relationship between otherwise disparate buildings, thus serving as a "protection against chaos".

The concept of style was foreign to architects until the 18th century. Prior to the era of Enlightenment, the architectural form was mostly considered timeless, either as a divine revelation or an absolute truth derived from the laws of nature, and a great architect was the one who understood this "language". The new interpretation of history declared each historical period to be a stage of growth for the humanity (cf. Johann Gottfried Herder's Volksgeist that much later developed into Zeitgeist). This approach allowed to classify architecture of each age as an equally valid approach, "style" (the use of the word in this sense became established by the mid-18th century).

Style has been subject of an extensive debate since at least the 19th century. Many architects argue that the notion of "style" cannot adequately describe the contemporary architecture, is obsolete and ridden with historicism. In their opinion, by concentrating on the appearance of the building, style classification misses the hidden from view ideas that architects had put into the form. Studying history of architecture without reliance on styles usually relies on a "canon" of important architects and buildings. The lesser objects in this approach do not deserve attention: "A bicycle shed is a building; Lincoln Cathedral is a piece of architecture" (Nikolaus Pevsner, 1943). Nonetheless, the traditional and popular approach to the architectural history is through chronology of styles, with changes reflecting the evolution of materials, economics, fashions, and beliefs.

Works of architecture are unlikely to be preserved for their aesthetic value alone; with practical re-purposing, the original intent of the original architect, sometimes his very identity, can be forgotten, and the building style becomes "an indispensable historical tool".