The 2014 Australian Academy of Science's Fenner Conference addressed the need for a steady state economy. We live on a finite planet after all and cannot have unending material 'throughput'. Indeed, there is a valid argument that degrowth of the economy is needed before we can achieve a steady state economy. Humanity has over-reached itself - we already require the resources of one and a half planets and yet human numbers and consumption keep growing. We have passed the limits to growth. Thus, mere stabilisation of human numbers is no longer enough. We must also 'degrow' before stabilising at a genuinely sustainable level.