Bisexuality is romantic attraction, sexual attraction, or sexual behavior toward both males and females,[1][2][3] or to more than one gender.[4] It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, which is also known as pansexuality.[5][6][7]

A bisexual pride flag

The term bisexuality is mainly used in the context of human attraction to denote romantic or sexual feelings toward both men and women,[1][2][8] and the concept is one of the three main classifications of sexual orientation along with heterosexuality and homosexuality, all of which exist on the heterosexual–homosexual continuum. A bisexual identity does not necessarily equate to equal sexual attraction to both sexes; commonly, people who have a distinct but not exclusive sexual preference for one sex over the other also identify themselves as bisexual.[9]

Scientists do not know the exact cause of sexual orientation, but they theorize that it is caused by a complex interplay of genetic, hormonal, and environmental influences,[10][11][12] and do not view it as a choice.[10][11][13] Although no single theory on the cause of sexual orientation has yet gained widespread support, scientists favor biologically based theories.[10] There is considerably more evidence supporting nonsocial, biological causes of sexual orientation than social ones, especially for males.[3][8][14]

Bisexuality has been observed in various human societies[15] and elsewhere in the animal kingdom[16][17][18] throughout recorded history. The term bisexuality, however, like the terms hetero- and homosexuality, was coined in the 19th century.[19]