Payments for environmental services (PES) are an innovative approach to conservation that has been applied increasingly often in both developed and developing countries. To date, however, few efforts have been made to systematically compare PES experiences. Drawing on the wealth of case studies in this Special Issue, we synthesize the information presented, according to case characteristics with respect to design, costs, environmental effectiveness, and other outcomes. PES programs often differ substantially one from the other. Some of the differences reflect adaptation of the basic concept to very different ecological, socioeconomic, or institutional conditions; others reflect poor design, due either to mistakes or to the need to accommodate political pressures. We find significant differences between user-financed PES programs, in which funding comes from the users of the ES being provided, and government-financed programs, in which funding comes from a third party. The user-financed programs in our sample were better targeted, more closely tailored to local conditions and needs, had better monitoring and a greater willingness to enforce conditionality, and had far fewer confounding side objectives than government-financed programs. We finish by outlining some perspectives on how both user- and government-financed PES programs could be made more effective and cost-efficient. © 2008 Elsevier B.V. All rights reserved.