This manual is a combination and revision from the assessment of sexual maturity stages developed for the PROS study on girls in 1995 and for the PROS puberty study on boys in 2005. It will assist the pediatric health care provider in learning how to assign the stages of the physical changes of pubertal development using the system described by Marshall and Tanner as well as correct techniques for breast palpitation and testicular measurement. This manual uses the classic photographs of Tanner and van Wieringen as well as many taken specifically for this resource.