While external knowledge has the potential to benefit a firm’s innovation activities, research shows that the positive effects of a more open model of innovation do not come naturally. This paper draws on the project level to explore the organizational factors that hamper or impede the integration of external knowledge sourced from an open innovation platform and to suggest interventions to overcome these barriers. While open innovation is mainly discussed as a concept that resides at the level of the organization, this paper draws on the project level to contribute to a multi-level understanding of open innovation and to offer a deeper understanding of the challenges project teams face, when integrating external knowledge. To investigate occurring barriers, four cases of external knowledge integration within a multinational corporation are analyzed. The results show that due to the external nature of the knowledge, an additional effort of project teams is required such as forming alliances with key individuals and changing negative attitudes towards external sources to overcome organizational resistance. Theoretical as well as practical implications are discussed.