Project-based ways of organizing are characterized by temporary structures, idiosyncratic work arrangements and non-routine, creative tasks. As such, projects hold great promise for learning and knowledge creation at the level of the individual participant, but their transient nature offers little support for the sedimentation of such learning within the organizational fabric. Project-based organizations therefore face a number of learning challenges. To address these challenges through the use of technology, this paper develops a design theory for technology-mediated learning systems that support learning processes in project-based organizations. Two organizations participated in our 30-month action research effort, which involved the generation of three design principles, the development of two design concepts, and the implementations of three prototypes and their empirical assessments. The design principles were derived from a kernel theory informed by theories of learning and distributed cognition.