The Chicago window was developed in 1895 by the American architect Charles B. Atwood.
The Chicago window is a large fixed glazing panel flanked by two narrower sashes of the same height. The large windowpane consist of a single panel of plate glass, and the flanking elements are vertical double-hung sash windows.
The window design was made possible by advances in glass-making technology, and became a defining feature of the Chicago school style. The design offered both abundant natural light and practical ventilation.