Puberty is a critical human development process that leads to sexual maturation and reproductive capability. It requires an intact hypothalamic pituitary gonadal axis (HPG). Any disruption of this axis can result in temporary or permanent disorders of reproductive endocrine function. The HPG axis is active during fetal development and continues to function in infancy until it enters a relative quiescent state. Pubertal onset is heralded by the re-emergence of the pulsatile secretion of hypothalamic GnRH. GnRH stimulates gonadotropin in the anterior pituitary gland to secret lutenizing hormone and follicle stimulating hormone that in turn bind to ligand specific receptors in the gonads , causing gonadal maturation and production of sex steroids, most notably testosterone and esradiol . This process is termed gonadarche. Testosterone and estradiol together with inhibin, activin and others regulate the subsequent activity of the hypothalamus and pituitary gland.Puberty is a dynamic period of physical growth, sexual maturation and psychosocial achievement that generally begins in boys between 9-14 years. The factors that regulate the onset of puberty remain elusive. Certainly, environmental and metabolic factors are critical regulators of HPG axis and the timing of puberty, but their influence on puberty is dependant on significant genetic control. Gene GPR54 appears to be a signal for the beginning of puberty in human beings. Leptin plays an important role in signaling nutritional status to the central reproductive axis and appears to be at least a permissive factor in the initiation of puberty. Combination of these factors lead to the pulsatile secretion of GnRH. Mutation in GPR54 in human causes hypogonadotropic hypogonadism, pubertal delay and sexual infantilism that can be corrected by administration of exogenous GnRH in pulsatile manner.The standard clinical system for describing normal pubertal development and its variations is the five stage system (Tanner staging). The Tanner stages of puberty are based on the development of the genitalia and pubic hair distribution.Testicular enlargement and increase in scrotal folds and pigmentation are the first clear signs of true puberty in boys. The onset of testicular enlargement occurs at age of 9.5- 13.5 year, then development of secondary sexual characters. Adrenarche is the puberty of the adrenal gland, the phenotypic result of adrenarche is pubarche or the development of axillary’s and pubic hair that appears in boys at about age 8 years. The phenomenon of adrenarche is unique to human beings.The sexual precocity is the appearance of any sign of secondary sexual maturation before the age of nine years in boys. Precocity due to early activation of the pulse generation of hypothalamic GnRH is known as central or GnRH dependant precocious puberty.On the other hand GnRH independent precocious puberty is due to a heterogeneous group of disorders which includes tumors that secret HCG and testicular or adrenal tumors that produce testosterone.We should interfere before the age of 9 years if there is any manifestation of precocity.In GnRH dependant precocious puberty, either organic causes as craniopharyngoma tumor which lies in Rathk’s pouch and secret LHRH and which leads to infertility and short stature should be excluded and surgically removed or functional causes.In this type of precocity give GnRH in constant manner to suppress HPG axis (e.g. leuporlide acetate and nafrelin acetate).In GnRH independent precocious puberty give steroid synthetase inhibitor (e.g. ketokonazole), antiandrogen (e.g. sprinolactone) and aromatase inhibitors (e.g. testolactone).In boys, absence of testicular enlargement by 14 years of age (volume < 4cc) defines as delayed puberty. In addition, delayed sexual development in boys is also defined as, slow progression of development or the passage of five years between the initial and the complete development of the genitalia. Delayed puberty is due to either hypogonadotropic hypogonadism (secondary), hypergonadotropic hypogonadism (primary) or Constitutional Growth Delay.In hypogonadotropic hypogonadism, Kallmann’s syndrome is the most common cause of isolated gonadotropin deficiency (hypogonadism with anosmia). Craniopharingoma the most common neoplasm in the hypothalamus pituitary area should be excluded early as it leads to either GnRH or gonadotropin deficiency. Early eradication of the tumor leads to satisfactory results.In hyperogonadotropic hypogonadism, the most common cause of gonadal failure is Klinefelter syndrome should be excluded clinically and by karyotyping. Sertoli cell only syndrome should be in mind. The diagnosis is mainly by testicular biopsy. Chronic illness and drug abuse should be asked in the history. Treatment of these disorders is still of guarded prognosis and ill satisfactory benefit to these patients.The most common cause of delayed puberty is constitutional delay of growth and maturation, which affect 53% of subjects of delayed puberty. Could be treated by sex steroid, short stature could be corrected especially in boys between 10-14 years and delayed puberty after age of 14 years old.However, early diagnosis and early proper interference in many cases cause better results with new advanced investigations and treatment.