Migrants are able to provide firms with knowledge about their country of origin. This can become a valuable source of knowledge for firms in the process of internationalization. Relating to a Knowledge-Based-View perspective, this paper explains how the resource commitment of firms to foreign countries is contingent on immigration from those countries: Immigrants’ country knowledge reduces uncertainty and makes the governance of foreign operations more efficient. Moreover, this paper connects the relevance of knowledge for firm internationalization to institutional characteristics in immigrants’ home and host countries, both of which policymakers can shape. We test predictions on more than 13,000 observations over a 14-year period (2003–2016). The paper identifies economically significant contingencies of a positive effect of immigration, which are robust to changes in model specification, measurement, and sampling. The results indicate how immigration can shape firms’ investments abroad and have implications for developing policy as well as international business theory. The full paper is available (open access) here: https://doi.org/10.1057/s42214-019-00034-9.