Abstract: Lobbying coalitions are a vital way for interest groups to work together in attempting to influence the policy process. Relatively little is known, however, about the internal workings of coalitions. This research investigates the provision of leadership within coalitions. It focuses on how inter-organizational networks influence which interest groups act as leaders in which coalitions. It stresses that relationships among interest groups promote reputation, encourage trust and distrust, and enhance communication and coordination on common projects. Using a Two-Mode Exponential Random Graph Model (ERGM) with structural zeros, it examines the effects of network dependence, size, communication, and content (indicated by partisan identities) on leadership, while accounting for alternative explanations related to organizational partisanship, resources, issue context, organizational structure, and age. The results demonstrate robust, positive effects of network dependence, communication, and content on leadership. This analysis yields significant insight on how interest groups engage in collective action when advocating their policy interests.