The enduring influence of the architect Gottfried Semper (1803-1879) derives primarily from his monumental theoretical foray <em>Der Stil in der technischen und tektonischen K�nsten</em> (1860-62), here translated into English for the first time. A richly illustrated survey of the technical arts (textiles, ceramics, carpentry, masonry), Semper's analysis of the preconditions of style forever changed the interpretative context for aesthetics, architecture, and art history.<br> Style, Semper believed, should be governed by historical function, cultural affinities, creative free will, and the innate properties of each medium. Thus, in an ambitious attempt to turn nineteenth-century artistic discussion away from historicism, aestheticism, and materialism, Semper developed in <em>Der Stil</em> a complex picture of stylistic change based on scrutiny of specific objects and a remarkable grasp of cultural variety. Harry Francis Mallgrave's introductory essay offers an account of Semper's life and work, a survey of <em>Der Stil</em>, and a fresh consideration of Semper's landmark study and its lasting significance.