Form and expression are basic notions in design aesthetics and design aesthetics education. This is something firmly rooted in architecture, product design, industrial design, fashion design and so forth, but how should we understand these notions in interaction design? There is a need here to fill a gap in the foundations of interaction design. This paper revisits “form” and “expression” to discuss the interpretation of these concepts in the context of interaction design aesthetics. The paper provides a general foundational discussion and considers the implications of relating interaction design to design aesthetics at a fundamental level, rather than to notions from behavioral and social science as is usual in the area of Human Computer Interaction.