The ten years since the financial crash have been lean years for progressive politics of all kinds. Now Brexit in the UK, Trump in the US, and the rising tide of national populism in Europe pose new dangers. Parties of the Centre-Left are in retreat. Old bases of support have declined, old policies are out of touch, old assumptions no longer hold. At the same time new thinking, new innovations, new forces are turning the world upside down. We face great dangers but also great opportunities. How should those who still want a progressive future respond? This book argues that the first priority is an Open Left. We must abandon the idea that one tradition of progressive thought has all the answers. We need openness to new policy ideas, openness to learning from past mistakes and other's experiences. We should be prepared to listen to very different voices and very different intellectual traditions. We must find ways to engage with people from a wide range of communities and backgrounds. An Open Left also recognizes we cannot retreat from the world, or ignore economic and political realities. We need a dialogue with progressive movements from many different countries, learning from their experiences of putting progressive ideas into action. The idea of progress can still inspire change, but it needs updating. This book is a contribution to that task.