Biological sex is multidimensional and relates to the physical characteristics by which a person is described as female, male or intersex. As a rule, such an attribution is assigned at birth, at the latest, on the basis of the child’s external and internal reproductive organs. Other dimensions of biological sex include genes and hormone balance. Contrary to common assumptions, however, biological sex is neither binary nor can it be clearly determined in every case. For example, there are intersex persons whose biological characteristics are not clearly female or male according to medical standards. The determination of medical norms for femininity and masculinity illustrates that biological sex, like gender, is also socially constructed.