The 2016 Lancet Early Childhood Development Series highlights early childhood development at a time when it has been universally endorsed in the 2030 Sustainable Development Goals. This series considers new scientific evidence for interventions, building on the findings and recommendations of previous Lancet series on child development (2007, 2011), and proposes pathways for implementation of early childhood development at scale. The series emphasizes “nurturing care,” especially of children below three years of age, and multi-sectoral interventions starting with health, which can have wide reach to families and young children through health and nutrition.