This article aims to reflect on the ASF-UK Change by Design methodology in participatory informal settlement upgrading, positioning it within ongoing debates about the conceptualization and practice of participatory design. The first part of this article draws on key literature exploring the relationship between participation and architecture and participation and design to identify the trends in the field of participatory design, especially those relevant to informal settlement upgrading. These trends are explored through their preoccupations with form/product, use, governance, and meaning. The article then identifies tensions in the conceptualization and practice of participatory design that have been particularly relevant to the elaboration of the Change by Design methodology. The second part of this article elaborates on key reflections emerging from the participatory design experience undertaken through the ASF-UK Change by Design workshops. These reflections serve as a potential conceptual lens to inform the positioning of participatory design practices in debates on the production of just cities from a critical urban theory perspective.