The family name is a part of the name of a person. It complements the first name and expresses the affiliation of the name bearer to a family.
As a rule, the expressions surname and surname are used synonymously. In Switzerland, one also says gender name (from family gender).
In contrast to the married name, the original family name acquired by descent is called the maiden name (in the case of married women also maiden name; in Switzerland, maiden name) and expresses the affiliation to the parental family. In many modern naming laws, birth names and married names can be combined in double names (Switzerland: alliance names). Artist's names can also be used as family names without a kinship reference. Contrary to what the expression "birth name" suggests, however, this name can change long after birth. In Germany, the birth name is defined as the name "which is to be entered in the birth certificate of a spouse at the time of the declaration [on the choice of a marriage name] to the registry office" (§ 1355Abs. 5 BGB), whereby it follows from the civil status law that the birth name noted in the birth entry can certainly change (§ 36 para. 1 PStV), namely through adoption, naming or official name change; only in the case of changes due to marriage, the birth name does not change, but a married name is acquired. In Switzerland this birth name is called Ledigname, in Austrian legal terminology it corresponds to the gender name.
The house name (farm name) fulfils a similar function as the family name in rural areas. In everyday language it is usually prefixed to the first name (call name), among others in Hesse, especially in southern Germany and Austria. If the surname is only used in correspondence, it is also called a spelling name. Historically, the woman was still addressed in writing in the 20th century with the first and last name of her spouse.
A person's surname can change in the course of life, for example through marriage, divorce, adoption or an official change of name. Involuntary adaptations are also possible, e.g. the adoption of the name of a new spouse by the premarital children of one of the partners, so that the new family can appear as a single unit in social and official dealings.
Naming is regulated very differently around the world and depends on culture, tradition, social order and origin (such as from nobility). Not all surname systems in Europe and the world employ family names. For example, in the Spanish-speaking world, the two-part surname (apellido, literally "call name") commonly used there is not a surname in the strict sense, because it does not recognize a common surname for members of a family. Instead, this system provides for an individual and invariable ancestral name (patronymic and matronymic) for each person, so that family members bear different surnames. Similar systems prevail in other countries, such as Italy. In this article, the different regional surname systems are dealt with even if, strictly speaking, they are not family names.