In recent decades, research has begun to examine the concept of the regional policy mix and its implications for regional innovation. While this has highlighted the role of interactions between multilevel policy instruments and the potential for duplication and synergies, it has tended to underplay the contribution of policy actors to managing such policy mix processes. This paper seeks to add to this literature by introducing the concept of boundary work, viewing it as a form of agency practice seeking to create, maintain, and disrupt instruments within the policy mix. Through a case study of digital technology diffusion instruments in Wales (UK), this paper examines the actors, practices, and effects of boundary work in the regional policy mix. The findings show that boundary work can help manage tensions in the policy mix through anticipatory practices but that complexity and uncertainty in the regional innovation policy mix present ongoing challenges to policymakers.