The IPCC Working Group III contribution to the Fifth Assessment Report (AR5) on climate change mitigation provides a comprehensive assessment of options for reducing greenhouse gas (GHG) emissions and limiting their atmospheric concentrations. Despite increasing mitigation policies, GHG emissions have continued to rise, with a significant acceleration in the last decade. The report highlights that stabilizing temperature increases within the 21st century requires a fundamental shift from business-as-usual practices. However, various emission pathways exist that could limit temperature increases to below 2°C relative to pre-industrial levels. These pathways, however, come with substantial technological, economic, and institutional challenges. Delayed mitigation efforts or limited access to low-carbon technologies further complicate these challenges. The report evaluates technical and behavioral mitigation options across energy, transport, buildings, industry, and land-use sectors, as well as policy options at different governance levels. It emphasizes the importance of sustainable development and equity in climate policy, recognizing that mitigation is just one of many objectives for decision-makers. The report also addresses the need for effective risk management, acknowledging that climate change mitigation can have both opportunities and risks, some of which are fundamental and difficult to manage. The report includes a wide range of scenarios, including those that aim to stabilize atmospheric concentrations at levels consistent with the 2°C goal. These scenarios involve a variety of technological, socioeconomic, and institutional trajectories, but uncertainties and model limitations remain. The report also discusses the potential for adverse side-effects of mitigation actions and the need for iterative assessment approaches. The report is structured into four parts, covering introduction, framing issues, mitigation pathways, and assessment of policies, institutions, and finance. It provides a detailed analysis of the drivers and trends in GHG emissions, the implications of different mitigation policies, and the challenges and opportunities associated with various mitigation pathways. The report concludes with a focus on the need for international cooperation, the role of governance structures, and the importance of investment and financing in achieving climate mitigation goals. The report is a critical resource for policymakers and the public, providing a transparent and comprehensive assessment of the scientific literature on climate change mitigation.The IPCC Working Group III contribution to the Fifth Assessment Report (AR5) on climate change mitigation provides a comprehensive assessment of options for reducing greenhouse gas (GHG) emissions and limiting their atmospheric concentrations. Despite increasing mitigation policies, GHG emissions have continued to rise, with a significant acceleration in the last decade. The report highlights that stabilizing temperature increases within the 21st century requires a fundamental shift from business-as-usual practices. However, various emission pathways exist that could limit temperature increases to below 2°C relative to pre-industrial levels. These pathways, however, come with substantial technological, economic, and institutional challenges. Delayed mitigation efforts or limited access to low-carbon technologies further complicate these challenges. The report evaluates technical and behavioral mitigation options across energy, transport, buildings, industry, and land-use sectors, as well as policy options at different governance levels. It emphasizes the importance of sustainable development and equity in climate policy, recognizing that mitigation is just one of many objectives for decision-makers. The report also addresses the need for effective risk management, acknowledging that climate change mitigation can have both opportunities and risks, some of which are fundamental and difficult to manage. The report includes a wide range of scenarios, including those that aim to stabilize atmospheric concentrations at levels consistent with the 2°C goal. These scenarios involve a variety of technological, socioeconomic, and institutional trajectories, but uncertainties and model limitations remain. The report also discusses the potential for adverse side-effects of mitigation actions and the need for iterative assessment approaches. The report is structured into four parts, covering introduction, framing issues, mitigation pathways, and assessment of policies, institutions, and finance. It provides a detailed analysis of the drivers and trends in GHG emissions, the implications of different mitigation policies, and the challenges and opportunities associated with various mitigation pathways. The report concludes with a focus on the need for international cooperation, the role of governance structures, and the importance of investment and financing in achieving climate mitigation goals. The report is a critical resource for policymakers and the public, providing a transparent and comprehensive assessment of the scientific literature on climate change mitigation.