This thesis investigates the social and technical complexity during the implementation of collaborative ICT innovation in the health sector and how these complexities are dealt with in practice. To this end, I conducted an in-depth case study of a collaborative ICT innovation project between a public hospital and a technology startup company in the health sector in Norway. The project aimed to implement a new mobile application that was meant to be used by clinicians to register and update patients data. It would replace the manual note taking process and supporting communication between clinicians during their workflow. The strategy for data collection was interviews, observations of meetings between the project actors, and viewing relevant documents. I used the theoretical lens of information infrastructure theory to analyze the complexity and how the project participants dealt with these complexities. Specifically, I use three concepts from the cultivation of installed base approach: Process orientation, User mobilization, and Learning. The findings highlight the socio-technical complexity of integrating a new mobile application in an installed base of existing clinical practices and information infrastructure. Also, the findings reveal the importance of the approach that the project followed, which started from the installed base. Targeting gradual and incremental changes, the flexibility of stakeholder mobilization after the concept development phase, along with continuous learning from the iterative engagements with the end-users, and informational and organizational experiences. The main contribution of this thesis is a suggested extension to the current Living Lab approach. The Living Lab approach is one of the fastest diffusing methodologies in Europe to manage collaborative ICT innovation. Based on concepts from cultivation theory and the findings, the extension I propose contains: first, better conceptualization of the ICT product when it is integrated with existing information infrastructure. Second, to extend the collaboration to go beyond the concept development phase and cover the implementation. Third, the complexity of the health sector with strict rules for patients privacy, indicates that the context may needs special attention when combining technical testing and co-creation activities with the users.