In both humans and mammals, sexual development is a long process. In most cases, the genetic sex (XX or XY) results in the development of the corresponding gonadal sex (ovaries or testes), which in turn secretes hormones that will masculinize or feminize the fetus. But throughout gonadal development, various accidents may occur, giving rise to a wide range of alterations and ambiguities. Disorders of gonadal development represent a heterogeneous class of sexual ambiguities caused by defects in gonadal development or a failure of testis differentiation.