This thesis investigates the effectiveness of agro-ecosystem based PES programs to provide ecosystem services and achieve poverty reduction. A case study from Tanzania known as the “equitable payments for watershed services (EPWS) program” piloted between 2008 and 2012 in Morogoro region has been used as the basis for an in-depth empirical study of an agro-ecosystem based PES program. The case-study approach has combined mixed methods quasi experimental research design and propensity score matching technique to prioritise attribution of the livelihood and environmental outcomes of the intervention, which remain under-utilized in evaluation of conservation interventions. The thesis findings provide insights that while the poor can participate in agro-ecosystem PES programs, their participation can be hindered by initial investment costs of inputs such as on manure, improved seeds, hoes and spades. Farm size, farmers’ access to information, participation in the design phase, and the change in farm management required by the program are significant determinants of program participation. Also, while PES payments contribute to local livelihoods, the indirect financial and non-financial benefits provide greatest contributions to livelihoods. In relation to additionality impact, program participation increases the number of sustainable land management practices and land under agro-forestry and reforestation amongst program participants. Furthermore, expected benefits such as crop yields from constructed terraces and manure, fire wood and timber products from agro-forestry and afforestation interventions are likely to increase the life span of the practices. The design of agro-ecosystem PES programs should include upfront payments in addition to other incentives which should be made timely in phases to ensure compliance. Local training and paraprofessional, external training and both enhancement of local formal and informal rules are essential to enhance the adoption of practices and to stop illegal activities such as forest reserve encroachment, illegal logging and fire.