Puberty is characterized by a series a hormonal events leading to the attainment of adult reproductive capacity. Clinical manifestations of the pubertal processes include breast development, pubic hair development, menarche and regular menstrual bleedings. Abnormal pubertal development includes a spectrum of disorders such as premature thelarche, premature adrenarche, central and peripheral precocious puberty, adolescent polycystic ovarian syndrome, functional ovarian hyperandrogenism, late-onset congenital adrenal hyperplasia, primary and secondary amenorrhea, and premature ovarian insufficiency. Diagnosis of these reproductive disorders includes biochemical as well as clinical evaluation. The biochemical evaluation of reproductive function includes measurement of basal reproductive hormone levels and dynamic pituitary or adrenal hormone testing. Correct interpretation of such test results requires detailed knowledge on the normal maturational changes in the hypothalamic-pituitary-ovarian and hypothalamic-pituitary-adrenal axes. Changes in basal reproductive hormone levels in infancy, childhood and adolescence as well as the GnRH and ACTH test procedures in girls and adolescents are described in this chapter.