While the term "Chicago School" is widely used to describe buildings in the city during the 1880s and 1890s, this term has been disputed by scholars, in particular in reaction to Carl Condit's 1952 book The Chicago School of Architecture. Historians such as H. Allen Brooks, Winston Weisman and Daniel Bluestone have pointed out that the phrase suggests a unified set of aesthetic or conceptual precepts, when, in fact, Chicago buildings of the era displayed a wide variety of styles and techniques. Other scholars have noted that the phrase implies that Chicago was the only locus of technical or aesthetic innovation in skyscraper design, when in fact developments in Boston, New York, Philadelphia and Cincinnati often paralleled or preceded similar work in Chicago. Contemporary publications used the phrase "Commercial Style" to describe the innovative tall buildings of the era rather than proposing any sort of unified "school".
Some of the distinguishing features of the Chicago School are the use of steel-frame buildings with masonry cladding (usually terra cotta), allowing large plate-glass window areas and the use of limited amounts of exterior ornament. Sometimes elements of neoclassical architecture are used in Chicago School skyscrapers. Many Chicago School skyscrapers contain the three parts of a classical column. The first floor functions as the base, the middle stories, usually with little ornamental detail, act as the shaft of the column, and the last floor or so represent the capital, with more ornamental detail and capped with a cornice.
The "Chicago window" originated in this school. It is a three-part window consisting of a large fixed center panel flanked by two smaller double-hung sash windows. The arrangement of windows on the facade typically creates a grid pattern, with some projecting out from the facade forming bay windows. The Chicago window combined the functions of light-gathering and natural ventilation; a single central pane was usually fixed, while the two surrounding panes were operable. These windows were often deployed in bays, known as oriel windows, that projected out over the street.
Architects whose names are associated with the Chicago School include Henry Hobson Richardson, Dankmar Adler, Daniel Burnham, William Holabird, William LeBaron Jenney, Martin Roche, John Root, Solon S. Beman, and Louis Sullivan. Frank Lloyd Wright started in the firm of Adler and Sullivan but created his own Prairie Style of architecture. Ludwig Mies van der Rohe, who had run the Bauhaus in Germany before coming to Chicago, is sometimes credited with the rise of a second "Chicago school" between 1939 and 1975.
The Home Insurance Building, which some regarded as the first skyscraper in the world, was built in Chicago in 1885 and was demolished in 1931. Some of the more famous Chicago School buildings include: