BECAUSE of the multiplicity of scientific disciplines studying physical development from a variety of angles and at many different levels with increasingly refined and ingenious methods and techniques (including radioactive isotopes deposited internally; implants; homografts, autografts, and heterografts; X rays; photographs including stereoscopic pictures in full color; vital staining; electroencephalography; and controlled experimentation of excellent design) the literature is tremendous. Only a small fraction of the published and pertinent research can be reviewed here. Emphasis will be placed on basic principles of growth and development.For those interested in research on human physical growth and development currently under way, the bulletins of the U. S. Department of Health, Education, and Welfare (94,95,96,97,98) will be of great value. For those interested in specialized aspects of physical growth, much pertinent material will be found in the annual reviews of physiology (36, 37, 38), medicine (77,78,79), and microbiology (11, 12).