Genome sequencing is one of the most exciting scientific breakthroughs of the past thirty years. But what precisely does it involve and how is it developing? In this brilliantly wide-ranging, one-stop guide WIRED journalist Rachael Pells explains the science behind genomics. She analyses its practical applications in medical diagnosis and the treatment of conditions that range from cancer to severe allergic reactions to cystic fibrosis. She considers its potential to help with advances in agriculture and environmental science. She explores the ethics of genetic modification and the dangers involved when humans 'play God'. And she addresses the fundamental question: to what extent will future advances transform human longevity and the quality of life.