The production of male gametes, i.e., spermatogenesis, takes place in the seminiferous tubules of the testis. This complex and highly efficient process takes approximately 2.5 months in humans and results in the formation of sperm, one of the most specialized cell types in the body, produced in quantities of tens to hundreds of millions per day. To sustain male fertility, spermatogenesis must be maintained at quantitatively normal levels. The seminiferous epithelium is in constant renewal: new cohorts of germ cells initiate differentiation at the basal lamina, while mature spermatozoa are released into the tubular lumen. Germ cell development follows a synchronized pattern, giving the epithelium a consistent appearance over time, referred to as the cycle of the seminiferous epithelium. Sperm production spans the reproductive life of males and depends fundamentally on the self-renewal of germline stem cells (GSCs). These are maintained within a niche formed by somatic cells and the surrounding microenvironment. The balance between GSC self-renewal and differentiation is essential for preserving fertility and perpetuation of the species. Sertoli cells, the somatic component of the seminiferous epithelium, provide the supportive microenvironment necessary for germ cell survival, proliferation, and differentiation. They are targets of follicle-stimulating hormone (FSH) from the pituitary and testosterone produced by Leydig cells under luteinizing hormone (LH) control. Sertoli cells translate these endocrine signals into paracrine cues that guide spermatogenesis and regulate gene expression in germ cells. While numerous hormones and growth factors influence spermatogenesis and GSC maintenance, FSH and testosterone are key regulators. FSH determines the sperm-producing capacity by setting Sertoli cell number, whereas testosterone is critical for male sexual differentiation, meiosis, and spermiogenesis. Ultimately, normal spermatogenesis—both in quantity and quality—relies on the synergistic action of FSH and testosterone.