Sir Dieter Helm discusses how we could shift to a sustainable economy. What would have to happen for this generation to live within its environmental means and to bequeath to the next generation a set of assets at least as good as it inherited? What would the sustainable economy look like? How do we stop climate change and biodiversity loss? Consumption would have to be on a sustainable growth path, having first ensured the proper capital maintenance of the infrastructures and the natural capitals. Polluters would have to pay, with prices reflecting the full costs of the pollution causes to make the stuff for us the ultimate polluters. Economic growth, driven by technological progress and ideas would continue, once the economy was put back to the sustainable level of consumption. This would be very different from what happens now. The focus would not be on Keynesian boosts to aggregate demand, borrowing for current consumption, and quantitative easing. Living within our - and hence the environment's means - would mean radical shifts in our life styles, changes to national accounting and to the frameworks of economic policy. Getting to the sustainable economy would be politically very difficult, but not doing so risks lots for climate change and further considerable destruction of biodiversity. Continuing on our current path is unsustainable: hence it will not be sustained.