Climate is a global common, and the task of reversing the worsening climate change is a global responsibility. There are two aspects to climate action: adaptation and mitigation. This paper focuses on mitigation, the global efforts for which are uneven as some countries are performing better than others. The paper evaluates the mitigation efforts of the G20 countries, which are collectively responsible for some 80 percent of global greenhouse gas emissions. The assessment is based on a composite Climate Performance Index which incorporates various dimensions anchored in the principle of ‘Common But Differentiated Responsibilities’. The exercise finds that India and Italy are the frontrunners in climate mitigation among the G20. This study can help outline the G20’s priorities in climate action, under India’s presidency.