Private foundations are the most common institutional form in global philanthropy and remain the principal philanthropic actors within global governance. A private foundation is defined by five features: non-profit and non-governmental status; tax exemption; a board of trustees/directors; an endowment and/or fund capitalized by a single individual, institution, or family; and distribution of funds, principally through grants, for charitable, educational, or religious purposes. Foundations have played a role not only in international relations, but also in the development of international relations theory, providing significant individual and institutional support to scholars and fostering research communities. The chapter explores the activities of foundations in the interwar era through to the present via an examination of areas in which private foundations have been most active. It examines key criticisms and controversies and provides a brief overview of emerging issues and future trends in global philanthropy.