The Maternal and Child Health Life Course Intervention Research Network and the Forum for Children's Well-Being at the National Academies of Sciences, Engineering, and Medicine jointly organized a webinar series to explore how mental health disorders develop over the life course, with a special emphasis on prenatal, early, middle, and later childhood development. This series centered on identifying gaps in our knowledge, exploring possible new strategies for using existing data to enhance understanding of the developmental origins of mental disorders, reviewing potential approaches to prevention and optimization, and proposing new ways of framing how to understand, address, and prevent these disorders from a life course development perspective. This publication summarizes the presentations and discussions from the series.