A person’s next of kin (NOK) is typically your closest living blood relative. However in the UK you do not have to be a blood relative to the person you appoint as your next of kin.
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 niece or nephew, first cousin, aunt or uncle, or grandparent.
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.
For the purposes of next of kin, adopted children are treated as blood relatives. However, relatives by marriage are never automatically considered next of kin.
