Technological diffusion is recognized as a key pillar of climate change mitigation in environmental agreements. This policy brief, Enhancing Technology Transfer and Diffusion, published as part of the Green-Win project, finds that enhanced technology transfers within a ‘climate club’ would have sizeable positive effects on GDP in a 2° scenario. Existing international policy measures such as the Clean Development Mechanism only had an impact on north-south diffusion and have mainly been directed to large emerging economies, mostly China, India, and Brazil. There exist major gaps in the network of technological diffusion, between and within developing world regions. Technology diffusion routes are much more influenced by long-term trade relationships existing between countries and by the level of technological development than by sectorial policy measures such as renewable support policy. In order to foster technological diffusion, climate clubs must target a major shift in the structure of international trade and economic integration. In developing countries, the build-up of a supply base of certain low-carbon technologies is as important as the deployment of the technologies.