The primary regulator of testicular function is the gonadotropin-releasing hormone (GnRH). This hormone is secreted in a pulsatile manner by hypothalamic neurons. GnRH stimulates the synthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary gland. LH stimulates the synthesis of testosterone (T) after binding to specific receptors on Leydig cells, whereas Sertoli cells within the seminiferous tubules are the target of FSH, leading to spermatogenesis. Hypogonadism results from a disorder of the testes (primary hypogonadism) or of the hypothalamic–pituitary axis (secondary hypogonadism) leading to associated signs and symptoms such as impaired sperm production, reduced libido and erectile function. Both may be congenital or acquired as the result of aging, testicular diseases, drugs or other extrinsic factors. Diagnosis is confirmed by measuring hormonal levels with different diagnostic workups for pre-pubertal and late-onset hypogonadism (LOH). This chapter aims to provide an overview of symptomatic hypogonadism and a detailed description of the management of the adult hypogonadal male.