Life is all around us, abundant and diverse, it is extraordinary. But what does it actually mean to be alive? Nobel prize-winner Paul Nurse has spent his career revealing how living cells work. In this book, he takes up the challenge of defining life in a way that every reader can understand. It is a shared journey of discovery; step by step he illuminates five great ideas that underpin biology. He traces the roots of his own curiosity and knowledge to reveal how science works, both now and in the past. Using his personal experiences, in and out of the lab, he shares with us the challenges, the lucky breaks, and the thrilling eureka moments of discovery. To survive the challenges that face the human race today - from climate change, to pandemics, loss of biodiversity and food security - it is vital that we all understand what life is.