The governance of climate change is in flux. In the understandable rush to explore what is filling the governance gaps created by gridlock in the international regime, scholars risk under-appreciating the capacity of states to engage in policy innovation at national and sub-national levels. Based on a review of existing concepts and theoretical explanations for (in)action at this level, we make the case for adopting a more holistic approach to understanding policy innovation, covering the source of new policy elements (‘invention’), their wider entry into use (‘diffusion’), and their projected and/or real effects (‘evaluation’). The analytical and methodological challenges that arise from integrating these three perspectives are systematically explored and integrated into a new analytical framework used in the other contributions to this volume to explore more fully the politics of invention, diffusion, and evaluation in specific areas of mitigation and adaptation policy.