An aesthetic doctrine applied to art and especially architecture developed in the early 20th century out of Chicago architect Louis Henry Sullivan's aphorism that form ever follows function. Functionalist architects and artists design utilitarian structures in which the interior purpose dictates the outward form, without regard to such traditional devices as axial symmetry or classical proportions. After WWI, the German Bauhaus produced a number of influential architects and designers, notably Walter Gropius and Ludwig Mies van der Rohe, who worked within this aesthetic.

Functionalism was subsequently absorbed into the International style as one of its guiding principles.