This paper extends the analysis of supply and demand determinants of innovation in energy-efficient technologies, accounting for international knowledge flows and spillovers. Using data on patents, we first show that geographical and technological distances are associated with a lower knowledge flow. We then construct measures for the internal and external knowledge stocks and present an empirical analysis of the supply and demand determinants of innovation accounting for knowledge spillovers across countries. Results confirm the role of both demand-pull effects and technological opportunity. In particular, we provide evidence that spillovers between countries have a positive impact on innovation in energy-efficient technologies.