Males primarily use testosterone as a sex hormone. Through its effects on the androgen receptor, it is released by the interstitial cells of the testes and is in charge of the male external genitalia development as well as the internal reproductive glands and ducts during adolescence and maturity. Additionally, testosterone is required for the descent of testes via the inguinal canal in the last 2 months of fetal development. When a Y chromosome and consequently the SRY gene are missing from an embryo, ovaries form. The Wolffian ducts do not mature because the fetal ovaries do not release enough testosterone. It is mostly used to treat male hypogonadism. Notably, this chapter addresses the following context: historical view of testosterone research, biosynthesis, secretion, metabolism, transport mechanism, biological actions, health benefit of testosterone, factors that promote and inhibit testosterone secretion, therapeutic implication as well as pathophysiology of testosterone secretion.