THE POLICY FORUM ABOUT THE PROPOSED Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) by C. Perrings et al. (â¿¿The biodiversity and ecosystem services science-policy interface,â¿� 4 March, p. 1139) refers to the role of the Platform in strengthening the science-policy interface in biodiversity and ecosystem services, but does not address the fact that science policy formation does not depend solely on scientifi c facts. In practice, policy is formed through the intermingling of scientifi c knowledge, political judgment, and practical considerations (1, 2). Establishing an institution to identify information, perform assessments, identify tools, prioritize capacity-building (3), and evaluate policy options will not necessarily provide a â¿¿robust â¿¦ science/policy interfaceâ¿� (4) because the science-policy interface is turbulent (5), not linear (1, 2, 6), and scientifi c input plays only a small role. The scientifi c information that policy-makers need derives from policy and political processes, not from scientistsâ¿¿ perceptions. The sciencepolicy interface can be bridged only when scientists understand this policy process and work with policy-makers to reduce political and policy risk, rather than simply providing scientifi c facts. IPBES has not met yet (the fi rst plenary session is scheduled in October 2011). Undoubtedly, IPBES will contribute to global understanding of biodiversity and ecosystem services, but the effectiveness of the Platform in operating across the sciencepolicy interface will depend on how well thescientists associated with IPBES understand the nature of policy.