Sexual orientation involves a person's emotional, romantic, and sexual attraction to individuals of a particular gender. It is divided into three main categories: heterosexual orientation referring to attraction to the opposite sex; homosexual orientation referring to attraction to the same sex, including gay (male-male attraction) and lesbian (female-female attraction); and bisexual orientation referring to attraction to both males and females. While the exact causes are unclear, most research indicates that sexual orientation is not a choice and that both biological/genetic factors and social environment play complex roles in determining a person's orientation. Issues related to sexual orientation include homophobia, discrimination against LGBT individuals, and the recognition of same-sex families and relationships.