Nonetheless, society has a legitimate interest in privileging those heterosexual unions that are oriented toward the generation and rearing of children.

The most common form of marriage is a legally binding heterosexual union.

Thirty-nine states have laws defining marriage as a heterosexual union.

Marriage on the Isle of Man applies only to heterosexual unions.

The compromise affirmed that "physical, sexual expression is appropriate only within the lifelong, monogamous, heterosexual union contracted in marriage."

Many other articles of the same law also assumes the marriage is a heterosexual union.

Since early in the 20th century, heterosexual civil unions (requiring two years of living together) have enjoyed the same rights as civil marriage.