A missing person is a person who has disappeared and whose status as alive or dead cannot be confirmed as their location and condition are unknown. A person may go missing through a voluntary disappearance, or else due to an accident, crime, or death in a location where they cannot be found (such as at sea), or many other reasons. In most parts of the world, a missing person will usually be found quickly. Criminal abductions are some of the most widely reported missing person cases.

By contrast, some missing person cases remain unresolved for many years. Laws related to these cases are often complex since, in many jurisdictions, relatives and third parties may not deal with a person's assets until their death is considered proven by law and a formal death certificate issued. The situation, uncertainties, and lack of closure or a funeral resulting when a person goes missing may be extremely painful with long-lasting effects on family and friends.

A number of organizations seek to connect, share best practices, and disseminate information and images of missing children to improve the effectiveness of missing children investigations, including the Missing Persons Center, the International Commission on Missing Persons and the International Centre for Missing & Exploited Children (ICMEC), as well as national organizations, including the National Center for Missing & Exploited Children in the United States, Missing People in the United Kingdom, Child Focus in Belgium, and The Smile of the Child in Greece.