This book shows how the ground for the current crisis in teen mental health was seeded by a decades-long shift from play-based childhoods to ones defined by over-supervision, structure, and fear: how adults began to overprotect children in the real world while unwittingly offering scant protection in the brutal online world. Haidt delves into the latest psychological and biological research to show the four fundamental ways in which a phone-based childhood disrupts development - sleep deprivation, social deprivation, cognitive fragmentation, and addiction - while offering concrete and scientifically based advice to parents, schools, universities, governments, and to teens themselves. Drawing on ancient wisdom and cutting-edge research, this eye-opening book is a life-raft and a powerful call-to-arms.