Sexism is a form of discrimination based on gender. While many people use the term specifically to describe discrimination against women, sexism can also affect men, intersexuals, and transsexuals, along with individuals who eschew traditional gender roles and identities, such as people who identify as genderqueer. Like other “-isms,” sexism has far-reaching effects in society, and the study of sexism is a complex field.

In addition to outright discrimination, sexism includes attitudes which support that discrimination, such as stereotyping sex roles and generalizing an entire gender. Sexism can be rooted in cultural traditions, fear, hatred, or superiority, with many sexists believing that their gender is superior, for a variety of reasons. While many nations have laws which are designed to thwart sexism in places like the workplace, sexism often infiltrates society so thoroughly that sexist attitudes cannot be easily shaken off.

Discrimination on the basis of gender can take a wide variety of forms. For example, some people believe that women should stay at home to focus on rearing children and keeping house, rather than pursuing professional careers. This attitude can lead to severe criticism when career women are involved, and as seen in the 2008 Presidential primaries, high-profile women are not exempt from sexism, even when they are running for the office of President of the United States. Others may feel that men should not pursue “women's work” such as nursing, teaching, or homemaking, criticizing men who pursue these activities.

It is also possible to see sexism from within a gender, in addition to criticism from the outside. Members of the same gender often criticize themselves with arguments which are rooted in sexism, as for example when women criticize each other for being too masculine and defying traditional ideas about gender roles and how women should behave. Sexism also manifests in language, as proved by the ample assortment of crude slang terms, most of which cannot be printed here, for women who defy the norm.

Sexism also does not occur in a vacuum. Sexism can be combined with ableism, racism, and other prejudices. Defeating sexism and other forms of discrimination often requires a great deal of personal courage, and a willingness to call others out on their behavior while recognizing such behavior in oneself. Sometimes the most powerful way to fight discrimination is to set an example yourself, showing critics that their ideas are baseless and proving that men can raise children, women can excel in mathematics and the sciences, and so forth.