Korean clans are groups of Korean people that share the same paternal ancestor. They are indicated by the combination of a bongwan () and a family name.
Korean clans distinguish families that happen to share the same family names. The bongwan identifies descent groups by geographic location of origin. For example, the Gyeongju Kim and the Gimhae Kim are considered different families, even though they happen to share the same family name Kim. In this case, Gyeongju and Gimhae are the respective bongwan of these clans. However, a clan name is not considered part of a Korean person's name, and it can be considered rude to call a person by their clan name, as families in Korea have one of the most meticulous and comprehensive systems of ancestry tracking in the world.
The bongwan and the surname are passed on from a father to his children, thus ensuring that person in the same paternal lineage sharing the same combination of the bongwan and the family name. A bongwan does not change by marriage or adoption.
Different family names sharing the same bongwan sometimes trace their origin to a common paternal ancestor, e.g. the Gimhae Kim clan and the Gimhae Heo clan share Suro of Geumgwan Gaya as their common paternal ancestor, though such cases are exceptional.
According to the population and housing census of 2000 conducted by Statistics Korea, there are a total of 286 surnames and 4,179 clans. The 2015 census reported that a total of 36,744 family clans exist among the 1,507 surnames extant in South Korea.
The Korean bongwan system was created from an adaptation of the Chinese family clan system. It is assumed to have been created around the late Silla and early Goryeo period as a result of Silla's sinicization policies. Taejo of Goryeo promoted the bongwan system to stably distribute a growing population and create a basis for tax revenue, whilst putting an end to the obsolete bone-rank system.
Numerous clans were created throughout local administrations of all sizes and statuses. Almost all Koreans, including the Yangmin and Cheonmin caste, identified with a bongwan from the early Goryeo to the Joseon period. A bongwan affiliated with a prosperous region was widely seen as a source of personal pride, while members from a lesser or impoverished bongwan often sought to escape their genealogical status. Changes in administrative divisions profoundly influenced the merging or creation of various clans.
During the mid-to-late Joseon Dynasty, poor Koreans (commoners and members of the "surname-less class") acquired surnames by purchasing the right to adopt them. Some even fabricated family trees (jokbo) to claim ancestry from prestigious clans. This phenomenon was influenced by government policies related to slaves and a desire to elevate their social status. By the time that the Joseon class system was officially abolished in 1894, nearly all Koreans had a surname.
Traditionally, a man and a woman in the same clan could not marry, so the combination of the bongwan and the family name of a husband had to differ from that of a wife. Until 1997, this was also the law, but this was ruled as unconstitutional.
When adopting a child, the adoptive father and the adopted child must share the same combination of the bongwan and the family name. However, in exceptional circumstances, adoptive parents can change an adopted child's family name for the adopted child's welfare. In this case, the adoptive parents must visit a family court to request permission to change the family name.