Large organizational projects must integrate the specific and dispersed knowledge of many individuals and groups to succeed. Thus, frequent exchanges between the project team and the organization's members are required. In this context, understanding of the knowledge integration process during cross-functional projects can be enhanced through the conceptual framework of social capital. A qualitative investigation of a French small firm conceptualizes knowledge integration as a three-phase model: collection, interpretation, and assimilation. The case shows that the integration process is cyclical with overlaps and inter-dependencies among the phases. This study leads to refinement of the social capital role in knowledge integration and reveals the dynamics of internal and external facets of social capital. That is, internal and external social capital play differentiated roles depending on the three phases of the knowledge integration process. Finally, the study reveals the co-evolution of social capital and knowledge integration as a resulting long-term effect.