Male infertility involves disruption of spermatogenesis, sperm transport, or sperm function. The HPG axis governs reproductive function: GnRH stimulates LH and FSH release; LH drives Leydig cell testosterone synthesis; FSH activates Sertoli cells to support spermatogenesis within the seminiferous tubules. Sertoli cells form the blood-testis barrier and secrete androgen-binding protein and inhibin (which provides negative feedback on FSH). Testosterone is converted to dihydrotestosterone (DHT) by 5-alpha reductase in target tissues, and to estradiol by aromatase. Pre-testicular causes include hypothalamic-pituitary dysfunction (hypogonadotropic hypogonadism, hyperprolactinemia). Testicular causes include Klinefelter syndrome, cryptorchidism, varicocele, chemotherapy-induced gonadotoxicity, and infection (orchitis). Post-testicular causes include obstructive azoospermia (vasectomy, congenital bilateral absence of vas deferens), ejaculatory dysfunction, and immunologic factors. The nurse performs comprehensive reproductive health assessment, coordinates diagnostic workup, manages medication protocols, and provides education and psychosocial support throughout the evaluation process.