The Working Group III contribution to the IPCC's Fifth Assessment Report (AR5) provides a comprehensive and transparent assessment of options for mitigating climate change through limiting or preventing greenhouse gas (GHG) emissions and reducing their concentrations in the atmosphere. Despite an increasing number of mitigation policies, GHG emissions have accelerated over the last decade. New mitigation scenarios suggest that stabilizing temperature increases within the 21st century requires significant departures from business-as-usual. Various emission pathways exist where temperature increases can be limited to below 2°C relative to pre-industrial levels, but this goal is associated with substantial technological, economic, and institutional challenges. The report assesses mitigation options across different sectors and governance levels, evaluating the societal implications of various mitigation policies. It highlights the importance of international cooperation and the need to address equity and justice in mitigation efforts. The report also discusses the role of risk management in climate policy and the potential co-benefits and adverse side-effects of mitigation actions. Overall, the findings enhance our understanding of the range of mitigation pathways available and their underlying requirements, providing crucial information for policymakers and negotiators working towards a new agreement under the UN Framework Convention on Climate Change in 2015.The Working Group III contribution to the IPCC's Fifth Assessment Report (AR5) provides a comprehensive and transparent assessment of options for mitigating climate change through limiting or preventing greenhouse gas (GHG) emissions and reducing their concentrations in the atmosphere. Despite an increasing number of mitigation policies, GHG emissions have accelerated over the last decade. New mitigation scenarios suggest that stabilizing temperature increases within the 21st century requires significant departures from business-as-usual. Various emission pathways exist where temperature increases can be limited to below 2°C relative to pre-industrial levels, but this goal is associated with substantial technological, economic, and institutional challenges. The report assesses mitigation options across different sectors and governance levels, evaluating the societal implications of various mitigation policies. It highlights the importance of international cooperation and the need to address equity and justice in mitigation efforts. The report also discusses the role of risk management in climate policy and the potential co-benefits and adverse side-effects of mitigation actions. Overall, the findings enhance our understanding of the range of mitigation pathways available and their underlying requirements, providing crucial information for policymakers and negotiators working towards a new agreement under the UN Framework Convention on Climate Change in 2015.