Orthographic projection has been, up to the appearance of 3D computer graphics, the almost exclusive representation method in engineering and the main one in architecture. Even in the computer age, applications managing three-dimensional models interact with users through orthographic representations shown in flat screens. However, in contrast with the huge literature devoted to linear perspective, historical studies about orthographic projection are surprisingly scant. This has led scholars to consider orthographic projection as a “natural” method, the elementary result of the elimination of the third coordinate. Quite to the contrary, historical evidence shows that orthographic projection was almost non-existent in Antiquity and the High Middle Ages, took form gradually in the Late Middle Ages on an empirical basis, and was progressively systematized in the Early Modern period and the Enlightenment. The present chapter will survey this historical evolution and will end by showing the ties of some episodes of the formation of computer graphics with one of the main focuses of the theory of orthographic projection, French technical schools.