How do long-distance commercial flight links affect social connectedness? Using a novel quantitative measure of friendship links developed by Bailey et al. (2018), we study how aviation affects the social ties between U.S. regions and foreign countries. To address issues of endogeneity between aviation and social connections, we employ instruments based on historical international passenger itinerary data. On a global level, we identify causal impact of aviation on social connectedness in 97 out of 140 countries with statistical significance. Moreover, we observe that the marginal benefit of flights on friendship seems to be highest in developing regions, suggesting that globalization and market integration attenuate the friendship benefits off lights in regions that are already well-connected and advanced in economic development. Four case studies reveal the importance of historical migration, diaspora, and linguistic communities on social connectedness in Brazil, Japan, Germany, and the UK.