Never before has it been so important for humanity to listen to science. A highly developed knowledge and advanced technology, unlike anything in history, provide the best conditions for determining the future of our planet. However, the decisions we make regarding the application of science cannot come from the laboratory; they must rather be the result of a broad public debate. Science must become part of our culture. As Martin Rees demonstrates in this expert and personal analysis, we need to think globally, rationally, and long-term, based on the technology of the 21st century, but guided by values that cannot be dictated by science.