Diagrammatics and interface studies have long been related. With diagrammatics, or diagrammatology, being the study of the epistemic properties of externalized relational signs, the connection between the two fields becomes clear: A graphical user interfaces (GUI), for example, relies on spatial distributions of semiotic elements. Such elements constitute an operational space in a medium and enable inferences and actions (iconicity, cf. Peirce). Connections between semiotic forms of information visualization, its operational principles, historical roots of diagrammatically organized interaction, and practices of designing diagrammatic encounters with technology are among this volume’s topics.