The article examines the politics and patterns of public-private partnerships for the environment in the multilateral system. It argues that two kinds of dynamics have contributed to the hybridization of environmental authority at the global level. On one hand, the fragmentation of environmental regimes and the parallel growth of non-state actors have resulted in structural pressures and opportunities for public-private collaboration. More significantly, however, international organizations have responded to the pluralization of global environmental politics selectively and acted as entrepreneurs of collaborative governance. The analysis uses a principal-agent perspective of international organizations to specify the conditions for organizational entrepreneurship of public-private partnerships. The theoretical propositions inform the comparative analysis of three "meta" partnership programs in the multilateral system: the Small Grants Program, the Prototype Carbon Fund, and the environmental portfolio of the United Nations Fund for International Partnerships. The study demonstrates that public-private partnerships represent neither a radical "powershift" from established institutions, nor are partnerships a marginal governance fad. The three partnership programs examined here emerged out of the mandates and expertise of their lead organizations and partners, but established and diffused new niches of environmental governance, particularly around community-based biodiversity management and climate-change related technology diffusion.