Throughout history, the force of gravity rendered the right angle sacrosanct in the world of architecture. However, as the 20th century dawned, the long-simmering diagonal motif finally arrived full force and upended the fields of architecture, design, and the fine arts. This book summarizes the author’s 60-year study of this revolutionary geometric motif and highlights how it is tied to social upheavals and artistic movements. Once people understand the concept of Diagonality, they will begin to see its angled planes on street corners, in art museums, and possibly in everyday objects. Diagonality has been all around us... but hidden in plain sight.