Payments for Ecosystem Services (PES) describes the situation where the user of an environmental service, such as water purification, pays the landowners who provide that service. For PES to exist, there must be a clearly defined user and supplier, as well as a number of other necessary conditions, which are defined in this document using a summary of current sources. Particular attention is paid to how these conditions currently obtain within the UNECE region. The range of forest environment services is explored through fourteen detailed case studies, which examine best practice in promoting PES. Political and public relations implications of PES are discussed at length, and recommendations include the need for clarity about where PES may be a useful tool in moving towards a green economy and where other methods may be more appropriate.