What is Next Of Kin?

Legal Definition
A person's next of kin (NOK) is that person's closest living blood relative or relatives. Some countries, such as the United States, have a legal definition of "next of kin". In other countries, such as the United Kingdom, "next of kin" may have no legal definition and may not necessarily refer to blood relatives at all.

In some legal systems, rights regarding inheritance (which imply a decision-making capacity — for example, in a medical emergency — where no clear will or instructions have been given, and where the person has no spouse) flow to the closest relative (regardless of the age, with a representative appointed if a minor), usually a child, a parent or a sibling. However, there are people without any close adult relatives and, in such a case, decision-making power often flows to a nephew, first cousin, aunt, uncle or grandparent.

For example, if a person dies intestate, the laws of some jurisdictions require distribution of the estate to the deceased's spouse or children. However, if there are none of these, the estate can often be distributed to the next closest group of living relatives, whether they be parents, grandparents, first cousins, aunts and uncles, or second cousins in extreme cases. If a person dies intestate with no identifiable next of kin, the person's estate generally escheats (i.e., legally reverts) to the government.

In cases of medical emergency, where a person is incapable (either legally because of age or mental infirmity, or because they are unconscious) of making decisions for themselves and they have no spouse or children, the next of kin may participate in medical decisions made by medical personnel, subject to the specific laws of the jurisdiction.

The inability of persons who are not in a legal marriage to make decisions with respect to the care of a live-in partner has resulted in many jurisdictions giving live-in partners rights equivalent to a spouse in such situations, even though most jurisdictions still do not require non-spouses to be made beneficiaries of estates (it is improper in most jurisdictions to disinherit a spouse). The inability of same-sex partners to have rights with respect to a partner's medical care or funeral arrangements over and above those of the next-of-kin is one of the main reasons behind litigation to require same-sex marriage or its equivalent.

For the purposes of next of kin, adopted children are treated as blood relatives. However, relatives by marriage are never considered next of kin.
-- Wikipedia
Legal Definition
This term is used to signify the relations of a party who has died intestate.

2. In general no one comes within this term who is not included in the provisions of the statutes of distribution. 3 Atk. 422, 761; 1 Ves. sen. 84. A wife cannot, in general, claim as next of kin of her husband, nor a husband as next of kin of his wife. But when there are circumstances in a will which induce a belief of an intention to include them under this term, they will be so considered, though in the ordinary sense of the word, they are not. Hov. Fr. 288, 9; 1 My. & Keen, 82. Vide Branch; Kindred; Line.
-- Bouviers Law Dictionary
Legal Definition
In the law of descent and distribution. This term properly denotes the persons nearest of kindred to the decedent, that is, those who are most nearly related to him by blood ; but it is sometimes construed to mean only those who are entitled to take under the statute of distributions, and sometimes to include other persons. 2 Story, Eq. Jur. § 1065b. The words "next of kin," used simpliciter in a deed or will, mean, not nearest of kindred, but those relatives who share in the estate according to the statute of distributions, including those claiming per stirpes or by representation. Slosson v. Lynch, 43 Barb. (N. Y.) 147.
-- Black's Law Dictionary
Legal Definition
Relatives in blood. See 72 N. Y. 312, 28 Am. Rep. 155.
-- Ballentine's Law Dictionary