This article contributes to our understanding of practices in innovating organizations. Previous studies have demonstrated how breakthroughs in knowledge may fail to be translated into practices if they are not aligned with existing practices, or if they cut across established boundaries and power structures. By drawing upon an ethnographic study of a medical R&D department that has been highly successful in developing new medical practices, this article investigates how such challenges can be overcome. To date, much of the literature has focused on coordination across single, well-defined boundaries. We here extend this focus and introduce the notion of ‘boundary organizing’ to analyse highly political and contingent processes of innovation and change within and across different practices. We add to existing literature by highlighting how the handling of multiple boundaries, the indirect effects of boundary work, the negotiation of mutual benefits and interests, and mutual adaptation are key aspects of boundary organizing.