Testosterone is the principal circulating androgen in human males, primarily synthesized within the Leydig cells of the testes. Biosynthesis of testosterone commences with the transport of cholesterol into mitochondria, followed by a series of enzymatic reactions catalyzed by steroidogenic enzymes. Following synthesis, testosterone may undergo further metabolism to dihydrotestosterone (DHT), a more potent androgen exhibiting enhanced biological activity. Contemporary research has identified alternative pathways for DHT biosynthesis, circumventing the conventional route involving testosterone as the immediate precursor. These novel pathways provide an alternate means of DHT generation, contributing to the overall androgen production. Androgens classically exert their effects through binding to androgen receptors (ARs), an interaction that initiates a cascade of events leading to transcriptional changes within target cells. The binding of androgens to ARs modulates gene expression, thereby influencing a broad spectrum of physiological processes. However, recent studies have revealed a non-classical mechanisms of androgen action involving membrane receptors. This alternative pathway permits androgens to elicit rapid, non-genomic effects, such as alterations in ion flux or activation of cellular signaling cascades. These immediate effects transpire independently of transcriptional changes and contribute to the multitude of physiological responses mediated by androgens. This chapter provides an examination of testosterone and related androgen biosynthesis, elucidating the critical enzymatic steps involved. Furthermore, it explores the diverse mechanisms of androgen action, encompassing both the classical nuclear receptor-mediated pathway and the recently identified non-genomic pathway. Additionally, the therapeutic implications of androgens, including clinical applications and potential adverse effects, are discussed. By delivering a comprehensive understanding of androgen biosynthesis, mechanisms of action, and therapeutic uses, this chapter aims to augment knowledge and inform clinical practice within the field of endocrinology.