Whereas mainstream economics is about expansion and productivity, environmentalism has often taken it upon itself to remind people of the limits and the consequences of exceeding them. Too many emissions will see climate catastrophe. Too much resource extraction will see society break down. But is this way of thinking counterproductive? Does appealing to external limits deny society the chance to set its own path? We spoke to the political ecology thinker Giorgos Kallis about his new book, Limits: Why Malthus Was Wrong and Why Environmentalists Should Care, to discuss problems with the standard discourse on limits and where to look for alternatives