Intersectoral partnerships have the potential to co-produce ‘synergistic’ solutions to complex public health problems, exceeding what any single organization acting alone might achieve. Synergy requires shared decision-making and equitable co-construction by partners. However, many partnerships struggle to realize such synergistic potential. Building on the Bergen Model of Collaborative Functioning, this study offers insights for optimizing partnership synergy by examining interactions between ‘inputs’ to the partnership—shared mission, and partner resources. Specifically, we introduce the concept of ‘dependency structure’ to draw attention to how these input interactions shape the balance of power and hence the potential for shared decision-making and co-construction. Findings are based on qualitative data from 10 intersectoral, health promotion partnerships in Denmark, including 27 interviews, 10 focus groups, partnership documents and meeting observations. We identified eight distinct types of ‘input resources’, which were important in shaping the potential balance of power between partners in more or less productive ways. However, the dependency structure that materialized—and its synergistic potential—was contingent on how these inputs interacted with the partnership mission. Our findings suggest a well-developed shared mission serves three functions—(i) foregrounding a common purpose, (ii) aligning individual partner’s self-interests and (iii) enabling action. The extent to which partnerships developed a shared mission serving all three functions influenced realization of a balanced dependency structure in which collaborators recognized their interdependencies, in turn promoting shared decision-making. To ensure the greatest potential for synergy, early and ongoing discursive processes to co-develop the partnership mission were particularly important.

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