This chapter deals firstly with the anatomy and physiology of male reproduction, and then gives an account of the aetiology and management of male factor infertility. The male reproductive system consists of the penis, testes, ejaculatory ducts and accessory sex glands. The testis produces the majority (6-7 mg/day) of testosterone, although a small amount is also produced by the adrenal glands. Spermatogenesis and synthesis of testosterone are under control of the anterior pituitary gland. Prior to investigating the infertile male, the clinician must ensure that the female partner has been thoroughly evaluated. The World Health Organization has defined the minimal semen parameters for fertility. These parameters are volume, pH, sperm concentration, total sperm number, motility and morphology. The surgical causes of male infertility include varicocele and cryptorchidism. The infertile male should be managed in a tertiary centre where appropriate facilities exist for microsurgery, assisted conception techniques and cryostorage of sperm.