This article proposes a framework for evaluating the development and evolution of economic instruments for environmental conservation through the examination of their design and the interactional and structural aspects of their implementation. The framework is applied to comparatively describe the historical evolution of the world's longest-running ecological fiscal transfer (EFT) scheme in two Brazilian sites. Results show that while legislative aspects of programme design, such as linkages and flexibility, are crucial for performance, interactional and structural characteristics during implementation, such as capacity, knowledge-sharing and transparency, can be determining factors in how the programme functions at the municipal level. Policy recommendations are provided for the development of this type of programme elsewhere. Results contribute towards the conceptual understanding of EFTs, an under-utilised mechanism with great potential for a role in conservation policy mixes.