Delayed puberty often causes considerable concern and anxiety, although in most cases, it results from a self-limiting variation of normal physiological timing, referred to as constitutional delay of growth and puberty (CDGP). Delayed puberty can, however, also be the first presentation of a permanent condition or a symptom of an underlying disease. Delayed puberty is defined as the absence of pubertal signs at an age of 14 years or more than two standard deviations (SD) above the population mean for pubertal onset. The underlying reasons for the large variation in age at pubertal onset are not fully understood; yet, nutritional status, as well as socioeconomic and environmental factors, are known to influence pubertal timing, and a significant number of genetic factors have also been identified. One of the main challenges in the diagnostic evaluation lies in differentiating benign CDGP from underlying pathological conditions such as hypogonadotropic hypogonadism (HH) and hypergonadotropic hypogonadism. Several methods have been investigated for this purpose and are reviewed in this chapter; though no single test has yet proven sufficient to reliably differentiate between the causes. Management of delayed puberty depends on the etiology. For boys with CDGP, an observational period will often reveal imminent puberty. If puberty does not progress spontaneously, sex steroid replacement is effective in stimulating the development of secondary sexual characteristics. There are several therapy options available for boys with hypogonadism, including sex steroid replacement. The long-term consequences of delayed puberty are both physical (e.g., reduced fertility and decreased bone mineral density) and psychological (e.g., low self-esteem) and emphasize the importance of careful clinical assessment of these patients.