["Journal of Management Studies, EarlyView. ", "\nAbstract\nEmerging ecosystem value propositions require collective co‐adoption by heterogeneous stakeholders. Focusing on middle managers (MMs) in ecosystem emergence, we introduce the notion of MM interface work: a form of social‐symbolic work comprising discursive, relational, and material micro‐practices within and across cognitive, behavioural, regulatory, and political interfaces. Drawing on rich primary and secondary data collected over 5 years from six technology providers in the healthcare sector, we explain how these micro‐practices underpin the co‐adoption of an emerging ecosystem value proposition. Two key mechanisms drive this process: the integration of micro‐practices within each interface and the synergistic alignment of the micro‐practices across interfaces. Our study advances ecosystem and strategic leadership literatures by explaining how MMs may influence co‐adoption of an emerging ecosystem value proposition ‘from the middle‐out’.\n"]