Climate change is the defining issue of our time and now is the defining moment to do something about it. There is still time to tackle climate change, but it will require an unprecedented effort from all sectors of society. To boost ambition and accelerate actions to implement the Paris Agreement on Climate Change, UN Secretary-General António Guterres will host the 2019 Climate Action Summit on 23 September to meet the climate challenge. The Summit will showcase a leap in collective national political ambition and it will demonstrate massive movements in the real economy in support of the agenda. Together, these developments will send strong market and political signals and inject momentum in the “race to the top” among countries, companies, cities and civil society that is needed to achieve the objectives of the Paris Agreement and the Sustainable Development Goals.