The paper discusses the economics of human development and social mobility, emphasizing the importance of early life conditions in shaping multiple life skills and the role of critical and sensitive periods in skill formation. It presents economic models that unify the treatment effect and family influence literatures, highlighting the empirical and policy importance of credit constraints in forming skills. The paper argues that untargeted income transfer policies to poor families do not significantly boost child outcomes. Mentoring, parenting, and attachment are essential for successful family interventions. The next wave of family studies will better capture the active role of the emerging autonomous child in learning and responding to the actions of parents, mentors, and teachers. The paper reviews recent empirical evidence on the expression and formation of capacities over the life cycle, highlighting eight key facts about human development and skill formation. These include the multiple skills that affect various life outcomes, skill gaps between individuals and socioeconomic groups, the role of genetics, critical and sensitive periods in skill formation, family investments, resilience and targeted investment, the importance of parent-child and mentor-child interactions, and high returns to early investment. The paper discusses the technology of skill formation, emphasizing the role of parental preferences and constraints in explaining the dynamics of family influence. It highlights the importance of complementarity between skills and investments, dynamic complementarity, and the role of parental skills in enhancing the productivity of investments. The paper also discusses the empirical challenge of analyzing family influence, the problem of the parent, and recent extensions of the basic model. It concludes that early investment in disadvantaged children is both socially fair and economically efficient, while later stage investments may not be as effective. The paper also discusses the role of credit constraints, the importance of parental skills, and the impact of income uncertainty on investment decisions.The paper discusses the economics of human development and social mobility, emphasizing the importance of early life conditions in shaping multiple life skills and the role of critical and sensitive periods in skill formation. It presents economic models that unify the treatment effect and family influence literatures, highlighting the empirical and policy importance of credit constraints in forming skills. The paper argues that untargeted income transfer policies to poor families do not significantly boost child outcomes. Mentoring, parenting, and attachment are essential for successful family interventions. The next wave of family studies will better capture the active role of the emerging autonomous child in learning and responding to the actions of parents, mentors, and teachers. The paper reviews recent empirical evidence on the expression and formation of capacities over the life cycle, highlighting eight key facts about human development and skill formation. These include the multiple skills that affect various life outcomes, skill gaps between individuals and socioeconomic groups, the role of genetics, critical and sensitive periods in skill formation, family investments, resilience and targeted investment, the importance of parent-child and mentor-child interactions, and high returns to early investment. The paper discusses the technology of skill formation, emphasizing the role of parental preferences and constraints in explaining the dynamics of family influence. It highlights the importance of complementarity between skills and investments, dynamic complementarity, and the role of parental skills in enhancing the productivity of investments. The paper also discusses the empirical challenge of analyzing family influence, the problem of the parent, and recent extensions of the basic model. It concludes that early investment in disadvantaged children is both socially fair and economically efficient, while later stage investments may not be as effective. The paper also discusses the role of credit constraints, the importance of parental skills, and the impact of income uncertainty on investment decisions.