Delayed puberty is defined as the absence of pubertal signs, in particular, increase in testicular volume (≥ 4 ml) in males and thelarche and menarche in females, at an age of 2–2.5 standard deviations more than for the normal population. This age for males is set at 14 years. Delayed puberty affects approximately 2.5% of adolescents, especially boys. In this chapter, dedicated to delayed puberty in males, starting from the characteristics of normal pubertal development, we have focused on the different causes of delayed puberty, recognizing the crucial importance of a differential diagnosis because from this derives the possibility of proposing personalized treatments, which can certainly lead to an improvement in the future quality of life of our young patients. The last paragraph of the chapter is dedicated to testicular dysgenesis syndrome, a multifaceted pathological condition that requires particular attention from reproductive physicians.