J PROD INNOV MANAG 2019;36(6):695–720 The Long and Winding Road: Building Legitimacy for Complex Social Innovation in Networks * Katrien Verleye , Helen Perks , Thorsten Gruber, and Joris Voets Social innovations, which increasingly take place in interorganizational networks, occur in environments character- ized by resource scarcity. To secure access to resources, social innovators need to establish legitimacy for their initia- tives. Yet, empirical work investigating the process of establishing legitimacy for social innovation—also known as legitimation—is absent. This research aims to uncover how legitimacy is established when social innovations are de- veloped, over time, through interorganizational networks. To investigate this process, the research adopts a longitudi- nal case study of a network of five market-leading organizations in the home care sector. A process-based analysis of evidence from 33 meeting observations, 45 in-depth interviews, and 249 documents reveals three novel findings. (1) The attainment of overall legitimacy depends on the establishment, over time, of three types of legitimacy targeted at different audiences. These are framed as building blocks oriented toward achieving interorganizational, multilevel, and external legitimacy. (2) The process of establishing legitimacy, across the building blocks, is underpinned by two dominant combinations of patterns—denoted as courting and demonstrating commitment. (3) Variation in two underlying mechanisms—conflicting tensions and role promotion—drives the enactment of these patterns across the different building blocks. The study’s novelty lies in the extrication of critical types of legitimacy and dominant pat- terns and mechanisms which underpin the process of establishing legitimacy. It contributes to social innovation and innovation legitimation literature by providing a deep-grained understanding of the process to establish legitimacy within social innovations carried out through interorganizational networks. Practitioner Points • Managers and policymakers should be cognizant of the need to establish three types of legitimacy when developing social innovations in interorganizational networks: interorganizational, multilevel, and exter- nal legitimacy. • To establish different types of legitimacy, social innovators are advised to iteratively engage in combinations of actions akin to courting and dem- onstrating commitment. • Managers should avoid trying to speed up the de- velopment of social innovation, as this can cause re- sentment and ultimately slow down the legitimation. • If policymakers want to stimulate social innovation in interorganizational networks, they should launch incentives for iterative re-engagement in courting and demonstrating commitment to key bodies. Introduction A ccess to and usage of basic services, such as health care, are essential to meet human needs. Yet, despite economic growth, these require- ments are not always guaranteed. The 2017 Global Monitoring Report, for instance, points out that half of the world cannot access basic health-care services (WHO-World Bank, 2017) and more than one quar- ter of the European population has unmet health- care needs (European Patient Forum, 2016; Eurostat, 2018). To address these types of unmet social needs, organizations increasingly engage in the development of multiple interdependent services with a social ob- jective (Spurrell, Araujo, and Proudlove, 2019). These social innovations are typically developed through a wide array of interested bodies operating in interor- ganizational networks and have been defined as new service constellations with a social objective (social NSCs; Agarwal and Selen, 2009; van Riel et al., 2013). Address correspondence to: Katrien Verleye, Center for Service Intelligence, Ghent University, Ghent, Belgium. E-mail: katrien. verleye@ugent.be. Tel: (+32) 9 264 3494. *The authors thank Prof. Dr. Angel Saz-Carranza and Prof. Dr. Joerg Raab—organizers of the workshop “Goal-Directed Networks: The State of the Art”—for the invitation to join this exciting event and the workshop participants for valuable comments. Additionally, the authors thank the Special Issue Editorial Team—Prof. Dr. Jelena Spanjol, Prof. Dr. Ruby Lee, and Dr. Sunny Li Sun—and three anonymous reviewers for their comments on earlier drafts of this paper. © 2019 Product Development & Management Association DOI: 10.1111/jpim.12506