This chapter advances the concept of diagrammatic social thought, building on the ideas of C. S. Peirce. First, I describe four approaches to visualizing theoretical ideas: cognitivist, constructionist, justificatory, and pragmatist. Second, I expand the classical pragmatist approach, linking Peirce’s “pragmatic maxim” with his semiotics of diagrams, in which diagrams represent objects via their skeletal relations. In this context, I argue that for theorists Peirce’s pragmatic maxim is a maxim to draw upon: by manipulating and experimenting with diagrams, we learn new things about our ideas. In this pragmatist conception, diagrammatic thinking is a form of relational and experimental thinking. Third, I analyze sociological theory diagrams. Based on ongoing research, I identify recurrent elements (arrows, lines, circles), types (path, network, cross-classification), and qualities (position, color, thickness) that depict a range of social relations and processes. Fourth, I explore “theorematic” reasoning: operations such as adding, removing, or modifying diagrammatic elements. These creative interventions shift a diagram’s affordances, altering relations among relations. I illustrate three theorematic techniques: adding forms, overlaying forms, and adding types. I conclude by reflecting on diagrammatic thinking’s underappreciated role in contemporary relational sociology and by highlighting intriguing lines of research to better integrate diagrammatic thinking into relational sociology.