The International Organization database is a new and unique source of information on the leadership characteristics of a large variety of international organizations over the last 25 years. The types of organizations included in the data includes multilateral organizations, transnational governance organizations of various kinds, and a variety of different global civil society organizations as well. The expansive sample of international organizations thus includes organizations that are composed completely of representatives with public authority, those with only private sector representation, and those that are hybrid in nature. The data is organized to allow future researchers, be they scholars, practitioners, or policy makers, to study a wide range of research questions on global affairs.