Nancy Bayley (28 September 1899 – 25 November 1994) was an American psychologist best known for her work on the Berkeley Growth Study and the subsequent Bayley Scales of Infant Development. Originally interested in teaching, she eventually gained interest in psychology, for which she went on to obtain her Ph.D. in from the University of Iowa in 1926. Within two years, Bayley had accepted a position at the Institute for Child Welfare (now called the Institute for Human Development) at the University of California, Berkeley. There she began the longitudinal Berkeley Growth Study, which worked to create a guide of physical and behavioral growth across development. Bayley also examined the development of cognitive and motor functions in children, leading to her belief that intelligence evolves over the course of child development. In 1954, Bayley began working on the National Collaborative Perinatal Project (NCPP) with the National Institute of Mental Health (NIMH), where she applied her work to infants. After retiring in 1968, Bayley synthesized her work and published the Bayley Scales of Infant Development, which is still in use today. For her efforts in the field of psychology, Bayley became the first woman to receive the Distinguished Scientific Contribution award from the American Psychological Association (APA), of which she was a fellow, amongst other honorary awards. Bayley was also a member of the American Association for the Advancement of Science. She died at the age of 95 from a respiratory illness.