Greens are driven by a concern with the fate of future generations and the natural world on which we all depend. They argue that theirs is the only way of ensuring the survival of a sustainable planet. The case they make is powerful, emotive, urgent and politically controversial. In the space of a couple of decades, Greens have shaped an influential movement. Issues such as climate change and biodiversity loss are now familiar and widely accepted.The challenge for Greens today is to turn mainstream rhetoric into meaningful action.