Puberty represents a period of important changes which lead to sexual maturation and active functions of reproduction. Sequences of the somatic and hormonal changes are presented both in boys and girls. Mean ages of onset of puberty are 10.9 and 11.2 in girls and boys, respectively. Menarche occurs at a mean age of 13.4 years and may be related to a critical weight. In boys, testicular growth above 4 cm2 or 4 ml is the first clinical sign of gonadal pubertal maturation. In girls, the first sign is the budding of the breast. At onset of puberty, the hypothalamus resumes a marked pulsatile secretion of gonadotropin-releasing hormone, leading to an increased secretion of pituitary gonadotropins which in turn stimulate the gonadal functions, i.e. the secretion of testosterone or estradiol and maturation of the spermatogenesis or the ovarian follicle. Neuroendocrine factors which probably control the onset of puberty are numerous: adrenergic or dopamine neurotransmitters, endogenous opioids, melatonin from the pineal gland. Gonadal maturation (gonadarche) is preceded in the infant by a postnatal surge of luteinizing hormone and at age 7-8 years by an adrenal maturation called adrenarche.