The notion of ecosystem services benefits from a strong support in international environmental agendas since last decade. Many scholars and experts advocate for mainstreaming it into national State policies, particularly in the conservation sector. However, neither the scientific evidence accumulated nor scholars' efforts to make the notion operational seem successful in influencing policies and their practitioners. This study looks at Costa Rica recent and current developments in adopting the notion of ecosystem services into sound policies in the conservation sector and the specific factors affecting this process. We looked at specific literature, documents and we undertook a series of qualitative interviews with civil servants and key individuals involved in conservation policies. We found that the adoption of ecosystem services notion remains sparse and disaggregated and follows the simultaneous influence of a conjuncture of cognitive, institutional, historic, juridical and cultural factors in a highly dynamic fashion. Our results suggest that scholars aiming at facilitating ecosystem services integration into specific policies should pay more attention to their context. (Résumé d'auteur)