Capitalism is arguably the most amazing cultural and economic product of humankind. It nurtured political liberty in Europe; it ushered in the industrial revolution in Britain and then around the world; it raised incomes everywhere; and it cleared away centuries of obscurantism and superstition. But it also brought into being a 'spirit of capitalism' that is individualist, expansive, acquisitive, ruthlessly rational and insatiable. This spirit has been responsible for commodifying relations and turning the natural world into a 'resource base' on the one hand, and a sink for wastes at the other. The industrial scale of this objectification and destruction of the natural setting has proceeded to the point where it is global, and now threatens our industrial civilization with collapse. My purpose in this paper is to sketch an account of how industrial capitalism might be 'naturalized', so that it continues to grow and deliver improvements in the quality of life without destroying humankind's resource base, and the biosphere as well. My focus is on rules and institutions rather than policies or prescriptions. My argument is that a green economy is already growing within the old, fossil-fuel economy, and that through competitive dynamics it will dominate by mid-century - unless blocked politically by vested interests.