Arnold Lucius Gesell (1880-1961) was an American psychologist and pediatrician whose pioneering research on the process of human development from birth through adolescence made a lasting mark on the scientific investigation of child development.

Arnold Lucius Gesell was born on June 21, 1880, in Alma, Wisconsin. His parents highly valued education, and early in his life, Gesell decided he wanted to become a teacher. He graduated from the University of Wisconsin in 1903 and then became a high school teacher and principal before entering graduate school at Clark University, where he received a Ph.D. degree in 1906. Gesell believed that in order to do research in child development, he also needed medical knowledge, so he studied medicine at Yale, receiving an M.D. in 1915. Early in his career he taught psychology and child hygiene at the Los Angeles State Normal School.

Gesell joined the faculty at Yale as assistant professor of...