Intermediary organizations have become increasingly prominent participants in education policy implementation despite limited knowledge about their distinctive functions and the conditions that constrain and enable those functions. This article addresses that research-practice gap by drawing on theories of organizational ecology and findings from a comparative case study of four intermediary organizations that helped with collaborative policy implementation in Oakland, California. I define intermediaries as organizations that operate between policymakers and implementers to affect changes in roles and practices for both parties and show that such organizations typically vary along at least five dimensions. Oakland's intermediary organizations all provided new implementation resources--knowledge, political/social ties, and an administrative infrastructure--but faced different constraining and enabling conditions. Using insights from this strategic case study, this article begins to build theory about intermediary organizations as important participants in contemporary policy implementation. (Contains 2 tables and 7 notes.)