**1. Introduction**

Payment for environmental services is understood as a mechanism to convert external/nonmarket values of the environment into actual funding to motivate those providing these ecosystem services (ES). In other words, payment for environmental services applies the benefit pays principle (BPP) to mobilize funds for environmental protection activities. Currently, payment for environmental services is being widely applied globally because this tool effectively protects environment and brings economic benefits to people.

In Vietnam, the program of payment for forest environmental services (PFES) was officially institutionalized through Decree No. 99/2010/ND-CP on "Payment for forest environmental services". After being promulgated, this policy has received great consensus from stakeholders and brought positive environmental and socio-economic effects. However, whether this policy has really become a new driving force for the protection and sustainable development of forests requires detailed evaluation. At the Conference summarizing Vietnam's PFES program after ten years of implementation, scientists and managers all agreed that Vietnam currently lacks an effective evaluation mechanism for the national program of PFES [1].

According to experts in the field of assessment of environmental services payment programs, there are three main terms used: *"Evaluate the results of the implementation of the policy" and "evaluate the implementation process of the policy"* and *"evaluate the effectiveness of the policy".* Which, the reviews of the program of payment for forest environmental services in Vietnam mainly focus on the first two aspects, while the third aspect has not been given due attention [2]. Sharing the same view, Ngai [3] said that Vietnam's state agencies mainly focus on the evaluation process of "Evaluating the implementation process" of PFES programs. In contrast, evaluations of the effectiveness and actual impacts of PFES programs on people's lives (social efficiency), benefits of economic (economic efficiency), and the effectiveness of forest protection (environmental efficiency) in fact have not been noticed. Faced with that situation, scientists and managers in Vietnam all agree that it is necessary to develop a method to evaluate the effectiveness of PFES programs in Vietnam. In this chapter, we introduce a method to evaluate the combined effectiveness of PFES programs based on a sustainable development approach (considering the program's sustainability based on three aspects of economy, society, and environment) with a case study in Ba Be district, Bac Kan province, Vietnam.
