A key feature of the humanoid social robot is its face. A robot face is not simply a technical choice, as faces communicate identity, affect and interpersonal spatial relations, and can be key to perceptions about the virtuousness of the robot. To address the significance of the robot face we develop a transdisciplinary reading of faces that compares how science, art and philosophy offer critical knowledges to inform the design of social robotics. Science understands face perception as a physiological, neurological and psychological process that perceives identity, emotion and spatial relations. Art provides a diverse repertoire of stylised faces in visual culture that reiterates the role of likeness, affect and social space. Art presents faces as ethically loaded, such as the war face, the blessed face and the abstracted face. Philosophy proposes the influence of a machine of faciality that abstracts the face as black holes on a white wall, invoking subjectivity and significance. In the second half of the paper we use qualitative visual analysis to develop a classification of robot faces: realistic; symbolic; blank; tech; and screen. We argue that design choice has philosophical, aesthetic and ethical consequences, as people are highly sensitive to the appearance, behaviour and social space of people, robots and their faces.