Book excerpt: A best-selling text, Understanding Motor Development: Infants, Children, Adolescents, Adults provides students and professionals with both an explanatory and a descriptive basis for the processes and products of motor development. Covering the entire life span, this text focuses on the phases of motor development and provides a solid introduction to the biological, affective, cognitive, and behavioral aspects within each developmental stage. The student is presented with the most up-to-date research and theory, while the Triangulated Hourglass Model is used as a consistent conceptual framework that brings clarity to understanding infant, childhood, adolescent, and adult motor development.