Marriage is the union of two individuals. Usually those individuals must be adults, but in some circumstances, minors as young as 15 years old may be married. There are other legal criteria to be eligible to be married, including that only non-blood related persons may get married and no party to the marriage may be presently married to another party. A marriage is essentially a type of contract, similar to two business partners going into business together. The law treats married persons differently from single persons in many regards, including tax treatment, dealings with children, rights upon a spouse’s death, and property ownership.