Brutalist architecture is an architectural style that emerged during the 1950s in the United Kingdom, among the reconstruction projects of the post-war era. Brutalist buildings are characterised by minimalist construction showcasing the bare building materials and structural elements over decorative design. The style commonly makes use of exposed, unpainted concrete or brick, angular geometric shapes and a predominantly monochrome colour palette; other materials, such as steel, timber, and glass, are also featured.

Descended from Modernism, brutalism is said to be a reaction against the nostalgia of architecture in the 1940s. Derived from the Swedish word nybrutalism, the term "new brutalism" was first used by British architects Alison and Peter Smithson for their pioneering approach to design. The style was further popularised in a 1955 essay by architectural critic Reyner Banham, who also associated the movement with the French phrases béton brut ("raw concrete") and art brut ("raw art"). The style, as developed by architects such as the Smithsons, Hungarian-born Ernő Goldfinger, and the British firm Chamberlin, Powell & Bon, was partly foreshadowed by the modernist work of other architects such as French-Swiss Le Corbusier, Estonian-American Louis Kahn, German-American Ludwig Mies van der Rohe, and Finnish Alvar Aalto.

In the United Kingdom, brutalism was featured in the design of utilitarian, low-cost social housing influenced by socialist principles and soon spread to other regions around the world, while being echoed by similar styles like in Eastern Europe. Brutalist designs became most commonly used in the design of institutional buildings, such as provincial legislatures, public works projects, universities, libraries, courts, and city halls. The popularity of the movement began to decline in the late 1970s, with some associating the style with urban decay and totalitarianism. Brutalism's popularity in socialist and communist nations owed to traditional styles being associated with the bourgeoisie, whereas concrete emphasized equality.

Brutalism has been polarising historically; specific buildings, as well as the movement as a whole, have drawn a range of criticism (often being described as "cold"). There are often public-led campaigns to demolish brutalist buildings. Some people are favourable to the style, and in the United Kingdom some buildings have been preserved.

The term nybrutalism (new brutalism) was coined by the Swedish architect Hans Asplund to describe Villa Göth, a modern brick home in Uppsala, designed in January 1950 by his contemporaries Bengt Edman and Lennart Holm. Showcasing the 'as found' design approach that would later be at the core of brutalism, the house displays visible I-beams over windows, exposed brick inside and out, and poured concrete in several rooms where the tongue-and-groove pattern of the boards used to build the forms can be seen. The term was picked up in the summer of 1950 by a group of visiting English architects, including Michael Ventris, Oliver Cox, and Graeme Shankland, where it apparently "spread like wildfire, and [was] subsequently adopted by a certain faction of young British architects".

The first published usage of the phrase "new brutalism" occurred in 1953, when Alison Smithson used it to describe a plan for their unbuilt Soho house which appeared in the November issue of Architectural Design. She further stated: "It is our intention in this building to have the structure exposed entirely, without interior finishes wherever practicable." The Smithsons' Hunstanton School completed in 1954 in Norfolk, and the Sugden House completed in 1955 in Watford, represent the earliest examples of new brutalism in the United Kingdom. Hunstanton school, likely inspired by Mies van der Rohe's 1946 Alumni Memorial Hall at the Illinois Institute of Technology in Chicago, United States, is notable as the first completed building in the world to carry the title of "new brutalist" by its architects. At the time, it was described as "the most truly modern building in England".

The term gained increasingly wider recognition when British architectural historian Reyner Banham used it to identify both an ethic and aesthetic style, in his 1955 essay The New Brutalism. In the essay, Banham described Hunstanton and the Soho house as the "reference by which The New Brutalism in architecture may be defined." Reyner Banham also associated the term "new brutalism" with art brut and béton brut, meaning "raw concrete" in French, for the first time. The best-known béton brut architecture is the proto-brutalist work of the Swiss-French architect Le Corbusier, in particular his 1952 Unité d'habitation in Marseille, France; the 1951–1961 Chandigarh Capitol Complex in India; and the 1955 church of Notre Dame du Haut in Ronchamp, France.

Banham further expanded his thoughts in the 1966 book, The New Brutalism: Ethic or Aesthetic?, to characterise a somewhat recently established cluster of architectural approaches, particularly in Europe. In the book, Banham says that Le Corbusier's concrete work was a source of inspiration and helped popularise the movement, suggesting "if there is one single verbal formula that has made the concept of Brutalism admissible in most of the world's Western languages, it is that Le Corbusier himself described that concrete work as 'béton-brut'". He further states that "the words 'The New Brutalism' were already circulating, and had acquired some depth of meaning through things said and done, over and above the widely recognised connection with béton brut. The phrase still 'belonged' to the Smithsons, however, and it was their activities above all others that were giving distinctive qualities to the concept of Brutalism."