Multisourcing—the delegation of interdependent tasks to multiple vendors—is receiving increasing attention in practice and in research. Yet, we know little about the circumstances under which organizations choose multisourcing. In this paper, we draw on incomplete contracting theory and the knowledge-based view to explain multisourcing decisions in application projects. We test our model using a comprehensive dataset of 1093 sourcing decisions made by Swiss public organizations. The results provide strong support for the model. We find that clients choose multisourcing more frequently when (1) the project is large, (2) the software is client-specific and the project is large enough, (3) client and vendor lack joint experience, (4) the client seeks knowledge, (5) the technology is not proprietary, and (6) the client is experienced in outsourcing. While these findings support common views that clients choose multisourcing in response to opportunistic threats and to knowledge needs, the findings also shed light on prerequisites for multisourcing.