This volume integrates and makes sense of the growing body of theoretical and empirical research conducted on purpose across the lifespan. It opens with a comprehensive yet detailed discussion of the definitions of purpose most commonly used in studies on the topic. In addition to defining the construct, the author also discusses its philosophical roots and distinguishes it from related concepts, including meaning, goals, and ultimate concerns. This volume discusses the disparate perspectives on the construct and addresses the tendency to position purpose in the broader frame of positive psychology. It synthesizes distinct strands of research on purpose across the lifespan, it explores studies on the daily and longer-term experience of a purposeful existence, and it delves deeply into the wide range of measurement tools that have been used to assess the purpose construct. Further, it examines the prevalence and forms of purpose among diverse groups of youth and discusses the developmental trajectory of the construct. Other topics discussed include the central role of purpose in supporting optimal well-being and positive youth development. The book closes with empirically-supported steps adults, educators, and mentors can take to effectively and intentionally foster purpose among young people and makes recommendations for future research on the topic.