The concept of environmental services (ES) has been rising during the last decade. It has led to new generation of mechanisms to cope with environmental issue in various countries. In the case of Costa Rica, which is considered as pioneer country in using the ES concept, its operationalization was done though a specific policy instrument: the Payment for Environmental Services program (PESP). Most of the existing literature put the emphasis on the innovation and learning process to describe this experience. Nevertheless it does not take into account the political dimension behind the emergence and implementation of Costa Rican PESP. Based on literature review and interviews of stakeholders, we analyse the policy process that have led to the emergence and evolution of the Costa Rican PSEP to derive lesson learnt for the improvement and extension of such policy instrument. We combine (i) the sequential approach of policy cycle to identify and describe the different phase of the emergence of Costa Rica PESP from the problem setting phase to the decision phase institutionalizing the program through the Costa Rican forestry law of 1997, and (ii) cognitive approaches of policy process analysis to identify the internal and external factors that have led to the emergence and evolution of this program. We show that, in the case of Costa Rican PESP, the policy steps were rapids from the agenda setting to the decision due to external constraints and internal compromises between leading actors in a context of dominance of one group of interest. We also show that the emergence was facilitated by an early problem setting on deforestation and the existence of relatively effective forestry incentive instruments as well as sectorial forestry organisations and institutions. We also shows that the initial architecture and governance rules of the program reflected the existing balance of power between various stakeholders of different sectors (forestry, agricultural, environmental) and