The European Union's vision of a single market is expanding to the free movement of research, innovation, data, and knowledge, an ambition that depends on effective cross-organisational collaboration and, consequently, on a high degree of interoperability. As organisations increasingly collaborate through Collaborative Networked Organisations (CNOs) and move into the digital domain, their success grows ever more dependent on the ability to interact towards mutually beneficial goals by sharing information, knowledge, and data. Yet despite considerable technical progress, many barriers to interoperability are institutional or governance-related rather than purely technical. Because research and practice continue to privilege technical solutions, the solution space remains narrow, and interoperability initiatives are undermined. This thesis therefore reframes interoperability as a governance challenge, consistent with the view of CNOs as socio-technical systems and adopts an Engineering and Policy Analysis perspective at the intersection of digital technologies and governance. It proposes commons scholarship, traditionally concerned with shared tangible resources but recently extended to intangible ones such as data and knowledge, as a lens for studying interoperability in CNOs, asking: how can commons scholarship inform the governance of interoperability in Collaborative Networked Organisations? Through two desk analyses and a case study, the thesis finds that interoperability is multidimensional yet often addressed in isolation; that only CNOs with a deliberate organisational structure and a long-term horizon are suited to a commons analysis; and that several commons frameworks, supported by the European Interoperability Framework, can systematically expose divergences between formal institutional arrangements and daily practice. The thesis contributes three replicable guideline tools, a decision tree, a set of application guidelines, and a checklist, demonstrated through a detailed case study. ... Read more