Prior research indicates that the relationship between top management team (TMT) faultlines and firm performance is equivocal. We shed new light on this topic by highlighting the moderating role of the CEO–TMT interface. Analyzing data from large international firms over the period 2005–2009 (347 firm-year combinations), we find that the performance effect of knowledge-based TMT faultlines is significantly altered when the leader of the TMT (i.e., the CEO): (a) socio-demographically resembles incumbent executives, (b) possesses a diverse career background, and (c) shares common socialization experience with other TMT members. Overall, our research reveals that different dimensions of the CEO-TMT interface play a pivotal role in determining the performance effects of knowledge-based TMT subgroups. Implications for upper echelons theory, team diversity, and strategic leadership research are discussed.