Building on a theory-based approach to synthesize research on the effectiveness of PES in achieving environmental objectives and socio-economic co-benefits, this article led by Jan Börner and published in World Development highlights the role of (1) contextual dimensions (e.g., political, institutional, and socio-economic conditions, spatial heterogeneity in environmental service values and provision costs, and interactions with pre-existing policies), and (2) scheme design (e.g., payment type and level, contract length, targeting, and differentiation of payments) in determining environmental and socio-economic outcomes. We also review counterfactual-based empirical evaluations, comparative analyses of case-studies, and meta-analyses. Our review suggests that program effectiveness often lags behind the expectations of early theorists. However, we also find that theory has advanced sufficiently to identify common reasons for why payment schemes fail or succeed. Moreover, payment schemes are often rolled out along with other policy instruments in so-called policy mixes. Advances in theory and evaluation research are needed to improve our understanding of how such policy mixes interact with the targeted social-ecological systems.