Global philanthropy is a significant source of financial resources in contemporary international relations, and it has provoked intense debates about the appropriateness of involving private foundations in global policymaking. Despite these facts, International Relations as a discipline has shown remarkably little reference to philanthropy as an important and relevant actor in global politics. In this article, I make the case for explicitly incorporating philanthropy into international relations analyses. Drawing on both historical examples and contemporary cases from the global health space, I show how philanthropy exerts a unique and independent influence within international society and that it needs to be understood holistically rather than focusing solely on individual philanthropic organisations. I also discuss how this expanding influence raises serious questions about accountability and legitimacy. Rather than making an argument about the appropriateness of philanthropy's involvement in international society, this article aims to make the case for philanthropy's analytical inclusion within the discipline.