In the World Library of Psychologists series, international experts present career-long collections of what they judge to be their most interesting publications – extracts from books, key articles, research findings, practical and theoretical contributions. Professor Richard M. Lerner has been prominent in the application of developmental science across the lifespan for half a century, investigating dynamic, relational development systems and their potential impact on positive youth development (PYD) and social justice. In this collection, Professor Lerner presents the development of his theory of, and research about, relations between life span, human development, and contextual or ecological change, exploring the mutually influential relations between humans and their peer, family, school, and community contexts. Including a specially written introduction in which Professor Lerner reflects on the importance of mentorship and contextualises both the field and the evolution of his wide-ranging career, this collection will be a valuable resource for students and researchers of developmental psychology.