This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book draws on developmental psychology in order to discuss knowledge in childhood and addresses children's acquisition of their first language. It introduces findings from the science of adolescent brains. The book analyses the value of childhood, proceeding through a number of distinctions between ways in which childhood can be valuable – intrinsically, and instrumentally – compared with non-existence or compared to adulthood, for the child herself or for others. It explains how the most influential accounts of autonomy entail that children can display it to a smaller or larger extent. The book also argues that genetic ties and sexual orientation do not make a difference to the quality of parenting.