Ecosystem services are the benefits humans receive from ecosystems and are the direct product of tightly coupled social-ecological systems. As human populations and consumption expand and wildlands shrink, ecosystem services, once plentiful and inexpensive, are increasingly scarce and costly. An innovative and rapidly emerging approach for sustaining the provision of ecosystem services is the creation of conservation payments designed to compensate land users who adopt practices that conserve or restore the ecosystems generating important services to society. Payments for hydrological services are arguably one of the most important and rapidly growing among publicly financed conservation programs, largely due to the critical situation of globally declining quality and quantity resources. PHS programs operate at the interface between the social, economic, and biophysical systems: While their overall objective is to enhance watershed sustainability by eliciting certain desirable decisions and actions in human-social systems driven largely by incentives from the associated economic systems, PHS programs often involve significant feedbacks, interactions, and tradeoffs between the different dimensions of coupled social-ecological systems, which may result in unpredictable effects on sustainability. Recent studies are starting to unravel the complex relationships between conservation payment policies and coupled social-ecological systems for a range of different ecosystem services and socioeconomic and cultural contexts. This symposium will emphasize emerging and novel research focused on enhancing interdisciplinary understanding of the complex interactions, feedbacks, synergies, and trade-offs among multiple dimensions of coupled social-ecological systems in response to conservation payment programs focused on hydrological services, and how these processes scale up to determine sustainability at the local, regional and global scales. In particular, we have structured the symposium to both highlight and integrate recent advances in research being conducted at the interface between conservation policy and science aimed at enhancing the provision of clean and plentiful water resources to society. Specifically, our goal is to bring together scientists (especially those actively participating in interdisciplinary research on complex problems) to discuss their findings and challenges from different perspectives, such as: quantifying the hydrological provided by different ecosystems, assigning “value” (e.g., monetary, cultural, quality of life, etc.) to those services, and integrating information from different ecological and human dimensions into meaningful metrics or indices that are useful policy makers. We have attached a preliminary list of potential speakers identified to date who would be invited to participate in this symposium upon approval by ESA.