Gender roles refer to the set of social and behavioral norms that are considered socially appropriate for individuals of a specific sex in the context of a specific culture, and which differ widely between cultures and historical periods. There are differences of opinion as to whether observed differences in behavior and personality between genders are entirely due to cultural or social factors, and are therefore the product of socialization, or to what extent gender differences are due to biological and physiological differences.

Views on gender-based differentiation in the workplace and in interpersonal relationships have often undergone profound changes as a result of feminist and/or economic influences, but there are still considerable differences in gender roles in almost all societies. It is also true that in times of necessity, such as during a war or other emergency, women are permitted to perform functions which in "normal" times would be considered a male role, or vice versa.

Gender has several definitions. It usually refers to a set of characteristics that are considered to distinguish between male and female, reflect one's biological sex, or reflect one's gender identity. Gender identity is the gender(s), or lack thereof, a person self-identifies as; it is not necessarily based on biological sex, either real or perceived, and it is distinct from sexual orientation. It is one's internal, personal sense of being a man or a woman (or a boy or girl). There are two main genders: masculine (male), or feminine (female), although some cultures acknowledge more genders. Androgyny, for example, has been proposed as a third gender. Some societies have more than five genders, and some non-Western societies have three genders – man, woman and third gender. Gender expression refers to the external manifestation of one's gender identity, through "masculine," "feminine," or gender-variant or gender neutral behavior, clothing, hairstyles, or body characteristics.