DescriptionUsing a sample of 58 science laboratory teams, this paper explores the impact of team demographic and informational diversity on team performance through the mediation of internal and external social capital in R&D teams. Diversity research has failed to find consistent results about the relationship between team diversity and performance. I argue that the mixed empirical results may be caused by the complex dynamics of internal and external networks in teams. Diverse teams may decrease team performance through reduced internal social capital and may increase team performance through increased external social capital. Therefore, the effects of team diversity on performance may be dependent on the extent to which the diversity impact on performance via external social capital (network size, social and job-related relationship, and network diversity) is higher than via internal social capital (social cohesion, job-related cohesion, trust, and cooperative norms). In addition, the effects of task characteristics (task interdependence and task routineness) on the relationships among social capital, diversity, and team performance were explored. Results showed that demographic diversity decreased internal social capital whereas informational diversity increased internal social capital. Both internal and external social capital increased team performance. Ethnicity/nationality diversity decreased team performance via reduced internal social capital and increased external social capital. The potential moderating effects of task characteristics were examined also. The moderating effects of task interdependence did not always show consistent patterns. However, for teams that performed non-routine tasks, I found stronger relationships between diversity and internal and external social capital compared to teams that performed routine tasks. In addition, for teams that performed non-routine tasks, I found stronger relationships between job-related internal and external social capital and team performance, compared to teams that performed routine tasks.