Innovation in public services is propelled by collaborations between public actors, private actors and service users. A substantial literature has centered on the benefits of user involvement in public services, but how user involvement can stimulate collaborative innovation is still largely unknown. This article develops and tests a theoretical framework based on the combined effect of 1) the empowerment of users, 2) specialized knowledge of the users, and 3) the absence of hindering rules and procedures. Data from 19 public-private eHealth collaborations in five European countries, collected through 132 interviews and 124 surveys, are analyzed through fuzzy-set Qualitative Comparative Analysis (QCA), and the results indicate that innovation in these partnerships is influenced by the combined effect of these conditions, but that this combined effect is also contingent on the roles the users adopt in the innovation process.