Transnational knowledge networks provide organizations with information useful in addressing shared problems. Social media may enable the formation of those networks, yet their role in the process has received little attention. This article examines the structure and antecedents of two networks facilitated by the microblogging platform Twitter operating in the policy domain of emergency management. One network includes national-level government agencies responsible for disaster response and recovery operations; the other includes nongovernmental organizations in the form of Red Cross and Red Crescent national societies. We use a logistic regression quadratic assignment procedure to test hypotheses derived from related literature. While findings indicate that shared language and geographic proximity shaped network formation, both networks exhibit boundary spanning behavior in which organizations sought out information from high-profile, resource-rich organizations. Those organizations helped to connect otherwise regionally bound clusters and demonstrate the nascent potential of social media to create global transnational knowledge networks.