There has never been a time when 'following the science' has been more important for humanity. At no other point in history have we had such advanced knowledge and technology at our fingertips, nor had such astonishing capacity to determine the future of our planet. But the decisions we must make on how science is applied belong outside the lab and should be the outcome of wide public debate. For that to happen, science needs to become part of our common culture. Science is not just for scientists: if it were, it could never save us from the multiple crises we face. For science can save us, if its innovations mesh carefully into society and its applications are channelled for the common good. As Martin Rees argues in this expert and personal analysis of the scientific endeavour on which we all depend, we need to think globally, we need to think rationally and we need to think long-term, empowered by twenty-first-century technology but guided by values that science alone cannot provide.