Surname, family name, or last name is the mostly hereditary portion of one's personal name that indicates one's family.

Depending on culture, the surname may be placed at either the start of a person's name, as the given name, or at the end. Depending on culture, not all members of a family unit are required to have identical surnames. In some countries, surnames are modified depending on gender and family membership status of a person. Compound surnames can be composed of separate names, such as in traditional Spanish culture.

Using names has been documented in even the oldest historical records. Examples of surnames are documented in the 11th century by the barons in England. English surnames began as a way of identifying a certain aspect of that individual, such as by trade, father's name, location of birth, or physical features, and were not necessarily inherited. By 1400 most English families, and those from Lowland Scotland, had adopted the use of hereditary surnames.

The study of proper names (in family names, personal names, or places) is called onomastics. A one-name study is a collection of vital and other biographical data about all persons worldwide sharing a particular surname.