As philanthropic foundations take on increasingly prominent socio-political roles, the need for stronger conceptualizations of foundations as an organizational form is articulated widely across academic, policy and practice contexts. Building on institutional research’s tradition of categorizing, classifying and typologizing organizational forms, our paper critically explores the different ways in which foundations have been cast and differentiated in international academic and practice literatures. Examining and integrating these, we propose an integrative framework of foundation types. Incorporating 13 categories – three contextual, five organizational and five strategic ones – the framework allows for clarifying distinctions and identifying commonalities between different foundation forms, offering a basis for developing more reflective and differentiated research and practice knowledge.