Over the past decade, the field of design for sustainable behaviour (DfSB) has gained agrowing amount of research interest. However, as the field evolves, new challenges also arise.A suitable unit of analysis is needed to contextualize users’ behaviour issues in a broadersocio-cultural and long-term perspective. This paper explores the use of activity theory(AT) as a potential lens for guiding empirical analysis and design exploration in DfSB. Byemploying a meta-synthesis approach, we systematically search and synthesize existingstudies that adopted AT in design for sustainability. Key findings show that AT’s principlesand theoretical implications are especially useful for helping design researchers frame andaddress DfSB challenges. We argue that by taking activity as the unit of analysis, the AT lenscan enable researchers to incorporate users’ dynamic, multi-level and complex activitysystems into DfSB considerations.