Follicle-Stimulating Hormone (FSH) is a gonadotropin, a type of hormone produced by the anterior pituitary gland, and plays a vital role in the regulation of the reproductive processes in both males and females. In women, FSH stimulates the growth of ovarian follicles in the ovary before the release of an egg at ovulation. In men, FSH is essential for spermatogenesis, the process of sperm production, which takes place in the seminiferous tubules of the testes. FSH works in conjunction with luteinizing hormone (LH), another gonadotropin produced by the pituitary gland. While LH primarily stimulates the production of testosterone by the Leydig cells in the testes, FSH acts directly on the Sertoli cells to facilitate sperm maturation. The levels of FSH in the bloodstream are regulated by the hypothalamic-pituitary-gonadal (HPG) axis through a feedback mechanism involving gonadotropin-releasing hormone (GnRH) from the hypothalamus and the sex steroids (testosterone and estrogen) produced by the gonads. Abnormal levels of FSH can indicate issues with the reproductive system, such as primary or secondary hypogonadism in men, or ovarian dysfunction in women. Measurement of FSH levels, therefore, plays a key role in diagnosing fertility issues and other conditions related to the reproductive system.