Human growth is a dynamic and complex process that begins with fertilization of the ovum and is completed with the fusion of epiphyses and metastases of the long bones marking the completion of adolescence. Growth occurs in phases with distinctive characteristics in terms of dominant influences from among genetic, environmental/nutritional, and hormonal factors and patterns. Prenatal growth is the most dramatic phase, achieving a velocity that is never again matched. It is predominantly under the influence of maternal size and nutritional status with little influence of parental genetic endowment. Insulin-like growth factors (IGFs) and insulin are critical, but thyroid hormone and growth hormone (GH) are not. Infancy is a period of rapidly changing growth rate, from 20 cm/year during the first few months to 10–12 cm/year by 1 year of age.