International advocacy NGOs (IANGOs) are increasingly important actors in the international arena. This paper provides a comparative analysis of the cases of ten IANGOs that operate in diverse advocacy contexts, including development, environment, governance, human rights, and constituent support. It examines the patterns of governance, organizational architecture, and advocacy effectiveness across the cases and generates six propositions that link governance, architecture, accountability, legitimacy, and effectiveness for such organizations. © 2011 Elsevier Ltd.