With the end of the Cold War, military security issues declined on the international agenda as environmental, economic, and social issues rose. As superpower conflict faded from the international agenda, space was created for new attempts at multilateral problem-solving. How have these changes affected the prospects for transnational organizing? Using data from the Yearbook of International Organizations this paper explores changes in the size, issue focus, geographic makeup, and organizational structure of the population of transnational social movement organizations (TSMOs) in recent decades. While not the only form of transnational cooperation, these formal organizations provide important infrastructures for sustained transnational political work. Key findings are that while the transnational social movement sector has continued to grow since the mid-20th century, its rate of growth has slowed in the 1990s. Also, human rights and environment predominate on TSMO issue-agendas, but during the 1990s more groups emphasized economic issues and adopted multi-issue organizing frames over single-issue focuses. Newer groups were more likely to be organized regionally, that is within the global North or South, which may reflect efforts to develop structures to better connect local settings with global networks.