Open service innovation enables business service firms to realize service innovations through engaging in external partnerships. The results of a review of studies investigating open innovation in a business service context indicate that prior work (1) primarily drew on a learning lens to explain service innovation and (2) adopted three levels of analysis, that is, alliance, alliance portfolio, and network, resulting in three disconnected research streams. In this chapter, we review each research stream and suggest future research opportunities. In addition, we suggest that factors tied to the three analysis levels directly and interactively influence service innovation. Therefore, we propose a multi-level open service innovation framework that can guide future research.