Bisexuality refers to sexual or romantic attraction toward members of both sexes. It is one of the three main classifications of sexual orientation, along with a heterosexual and homosexual orientation, which all three together form the heterosexual-homosexual continuum.

According to Alfred Kinsey's research into human sexuality in the mid-20th century, most humans do not fall exclusively into heterosexual or homosexual classifications but somewhere between. The Kinsey scale measures sexual attraction and behavior on a seven-point scale ranging from 0 ("exclusively heterosexual") to 6 ("exclusively homosexual"). According to Kinsey's study, most persons fall within the range of 1 to 5 (a mixture of heterosexual and homosexual). Although Kinsey's methodology has come under criticism, the scale is still widely used in describing the phenomenon of bisexuality.

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