Get the science right when paying for nature's services.

In this article the authors discuss the importance of integrating scientific knowledge and methods into payments for ecosystem services (PES). They discuss the challenges of identifying whom to compensate, what to pay, how much to pay, and the mechanisms for payment, the variation of scientific content of PES programs and projects, and the establishment of standards. A framework for integrating natural science into PES, based on six natural science principles, is presented.