Gender identity is a person’s private sense, and subjective experience, of their own gender. This is generally described as one’s private sense of being a man or a woman, consisting primarily of the acceptance of membership into a category of people: male or female. All societies have a set of gender categories that can serve as the basis of the formation of a social identity in relation to other members of society. In most societies, there is a basic division between gender attributes assigned to males and females. In all societies, however, some individuals do not identify with some (or all) of the aspects of gender that are assigned to their biological sex. In most Western societies, there exists a gender binary, a social dichotomy that enforces conformance to the ideals of masculinity and femininity in all aspects of sex and gender: biological sex, gender identity and gender expression. Some societies have third gender categories that can be used as a basis for a gender identity by people who are uncomfortable with the gender that is usually associated with their sex; in other societies, membership of any of the gender categories is open to people regardless of their sex. Gender identity is usually formed by age three and is extremely difficult to change after that. The formation also commonly concludes between the ages of four and six. Gender identity is affected by influence of others, social interactions, and a child’s own personal interest. Understanding gender can be broken down into four parts: (1) understanding the concept of gender, (2) learning gender role standards and stereotypes, (3) identifying with parents, and (4) forming gender preference. A three year old can identify themselves as a boy or a girl, though they do not yet fully understand the implications of gender. Gender identity is formed as children search for social cues and display approval for others based upon the gender with which the child identifies, though gender identity is very fluid among young children. Studies suggest that children develop gender identity in three distinct stages: as toddlers and preschoolers, they learn about defined characteristics, which are socialized aspects of gender; the second stage is consolidation, in which identity becomes rigid, around the ages of 5–7 years; after this “peak of rigidity,” fluidity returns and socially defined gender roles relax somewhat.