Male sexual differentiation is the result of complex mechanisms involving developmental genetics and endocrinology. Formation of the bipotential gonads and subsequently the testes is dependent on a series of sex chromosome-linked and autosomal genes. The testes secrete both peptide and steroid hormones essential for the formation of internal and external genitalia. Hormone action is mediated via specific receptors, functioning as transcription regulators. Disruption of these genetic events leads to sexual dimorphism involving external and internal genitalia, and may also interfere with the development of other organs.