Paying for the provision of environmental services is a recent policy innovation attracting much attention in both developed and developing countries. This innovation, referred to as ‘payments for ecosystem services’ (when the emphasis is on enhancing ‘nature’ services) or ‘payments for environmental services’ (when amenities provided by the built environment are also included) is referred to here as PES. PES programs aim to harness market forces to obtain more efficient environmental outcomes. Since so many opportunities for PES programs could involve farmers in poor regions, international aid agencies and private donors, looking for a double dividend, increasingly consider using PES programs as a potential way of meeting both social and environmental objectives.