To the many adolescents who have generously shared their time with me across therapy rooms, research labs, and classrooms: thank you for everything you have taught me. – JN
To my newborn son Henry. I can’t imagine what digital media will be like when you’re a teen, but I hope the science we continue to do will equip parents to help teens thrive in digital spaces. – EHT
To my own children, Samara and Max, who will ask me for smartphones soon, and to my wife, Tina, who will remind me of this book and help me say “no.” – MJP