Of course, not all our decisions about the future are in tune with what economic rationality would like us to do. We promote evidence-based decision-making, but of course there is no evidence about the future. Moreover, experience shows that simply extrapolating from the past can be ridiculous, dangerous or at best misguided.A complexity approach helps us to avoid these errors. We are dealing with a world characterised by nonlinearities, tipping points, and asymmetrical relations where a small cause can have a big effect. In a systems approach, global issues need global solutions. Environmental problems do not respect borders.You need to import some goods and services to be able to export others. The digital revolution is making it hard to define what the “domestic” in “gross domestic product” is. Growing inequalities are creating discontent.If we are to tackle these issues, governments must change the ways in which they design and implement policies. An acceptance of complexity shifts governments from a top-down siloed culture to an enabling culture where evidence, experimentation, and modelling help to inform and develop stakeholder engagement and buy-in.