The relationship between the international mobility of academic researchers and social capital is complex. On the one hand, the literature suggests that social capital facilitates the international mobility of academics which, in turn, promotes the accumulation of international social capital, enhances research productivity, and advances careers. On the other hand, international mobility can isolate researchers from the national social capital in their origin countries. In this paper, I present the results of 42 interviews in Canada and Germany to examine how academics in both countries have experienced the connection between international mobility and social capital. In addition to revealing the complexity of this connection, the results show that social capital facilitates international mobility and that mobility sometimes creates social capital. However, mobility can also lead to the loss of national social capital that negatively affects early-career researchers in particular.