What does it mean to be secure in the 21st century? Mark Beeson argues that some of the most influential ideas about global security, including the troubling re-emergence of 'spheres of influence', are outdated products of earlier times that are inappropriate for the modern world. At a time when climate change poses an existential threat to the continuation of life itself, Beeson argues that there is an urgent need to rethink security priorities while we still can. Providing an explanation of the failures and dangers of the conventional wisdom, he outlines the case for a new approach that takes issues like environmental and human security seriously.