Gender identity is the psychological denomination of one's own sexual identity and the belief or consciousness that one belongs to a gender. The English term was introduced by the American psychologist and sexologist John Money. [1] [2]

It is agreed that core gender identity is formed by age two. The chromosomal sex, the endocrine (hormonal) constitution of the body, the development of internal and external genitalia, the gender-specific brain distinction and the so-called assigned gender play a decisive role in the development of gender identity.

The most common gender identities are the two distinct, opposite forms of masculine and feminine. [4] [5] The two opposites have been depicted since ancient times such as by Platon. [6] According to Thomas Lacquer's thesis, the dualism theory has become popular as from the 18th century. [7] [ONE-SEX-MODEL] Nowadays, there are books like „Men are from Mars, Women are from Venus" but are men and women really so different? What happens to those who cannot be assigned to a clear gender identity? [8]

It seems as if questioning and exploring gender identity is often perceived as attack on one's own gender role. [9] At the same time, the discovery and reflexion of one's (gender) identity can be experienced as interesting process and experience which can enrich life and open new perspectives.