Based on an extensive literature review and research interviews of energy experts, this article asks: what are the remaining impediments to clean energy systems and how can a Post-Kyoto Protocol climate framework be designed to overcome them? The article begins by exploring commercially available 'clean' energy systems and practices relating to energy end-use and infrastructure, energy supply, carbon capture and storage, and non-CO2 related greenhouse gas emissions. The article then examines a selection of persistent financial, market, information and intellectual property barriers. Lastly, it articulates the implication of these barriers for the design of future national and international climate change policies.