This paper analyses the role of official development assistance (ODA) in the evolution of Technological Innovation Systems (TISs) of improved cookstoves in Kenya and Rwanda. Functionally balanced TISs are central to the diffusion of new technologies and practices. We find that ODA has significantly influenced major innovation activities related to improved cookstoves in both Kenya and Rwanda over the last 30 years. However, donors' funding has been focused mainly on the development and diffusion of technical knowledge. We find that this pattern of ODA support has not fostered balanced and effective Technology Innovation Systems, and that this has contributed to the failure to achieve widespread diffusion of improved cookstoves. We develop a quasi evolutionary model for the long-term and systematic ODA support of innovation systems to build sustainable renewable energy TISs in developing countries.