Puberty is the biological transition from childhood to adulthood. The process involves the coordination of hormonal, physical, psychosocial, and cognitive systems to result in physiologic change. Precocious puberty is defined as pubertal development beginning earlier than expected based on normal standards. Gonadotropin dependent precocious puberty is caused by premature activation of the hypothalamus resulting in pulsatile secretion of GnRH. Gonadotropin independent precocious puberty is caused by excess sex hormones from peripheral or external sources. Treatment with GnRH agonists should be offered to prevent early fusion of the epiphyseal plates to avoid unnecessary short stature and should not be based on perceived psychosocial consequences of early puberty. Delayed puberty is the absence of or incomplete development of secondary sexual characteristics. Hypergonadotropic hypogonadism or primary hypogonadism may result from genetic mutation syndromes or can be acquired from antiovarian antibodies, exposure to radiation or chemotherapy, inflammatory insult, or surgical removal of the gonads. Hypogonadotropic hypogonadism or secondary hypogonadism is due to hypothalamic dysfunction resulting in impaired secretion of GnRH. The long-term goal for patients with inadequate estrogen stimulation is to maintain the serum concentration of sex steroids within the normal adult range to promote the development of secondary sexual characteristics, prevent premature bone loss, and ultimately to induce fertility when indicated.