Diagrams are essential in most fields of human activity. There is substan­ tial interest in diagrams and their use in many academic disciplines for the potential benefits they may confer on a wide range of tasks. Are we now in a position to claim that we have a science of diagrams-that is, a science which takes the nature of diagrams and their use as the central phenom­ ena of interest? If we have a science of diagrams it is certainly constituted from multiple disciplines, including cognitive science, psychology, artificial intelligence, logic, mathematics, and others. If there is a science of diagrams, then like other sciences there is an appli­ cations, or engineering, discipline that exists alongside the science. Applica­ tions and engineering provide tests of the theories and principles discovered by the science and extend the scope of the phenomena to be studied by gen­ erating new uses of diagrams, new media for presenting diagrams, or novel classes of diagram. This applications and engineering side of the science of di­ agrams also comprises multiple disciplines, including education, architecture, computer science, mathematics, human-computer interaction, knowledge ac­ quisition, graphic design, engineering, history of science, statistics, medicine, biology, and others.