Cohen (Hebrew: כֹּהֵן, romanized: kōhēn, lit. 'priest') is a surname of Jewish, Samaritan and Biblical origins (see: Kohen). It is a common Jewish surname, and is the most common surname in Israel.

Bearing the surname often (although not always) indicates that one's patrilineal ancestors were priests in the Temple of Jerusalem. Although not all Kohenic lines stem from Aaron, the brother of Moses, he is generally regarded as the patriarch of the lineage and the first Kohen. A single such priest was known as a Kohen, and the hereditary caste descending from these priests is collectively known as the Kohanim. As multiple languages were acquired through the Jewish diaspora, the surname acquired dozens of variants. Not all persons with related surnames are kohanim, and not all kohanim have related surnames.

Some Kohanim have added a secondary appellation to their surname, so as to distinguish themselves from other Kohanim—such as Cohen-Scali of Morocco, who trace their lineage to Zadok, and Cohen-Maghari (Meguri) of Yemen, who trace their lineage to Jehoiarib, one of the priestly divisions.

Being a Kohen imposes some limitations: by Jewish law a Kohen may not marry a divorced woman and may not marry a proselyte (someone who converted to Judaism). Nor should an observant Kohen come into contact with the dead or enter a cemetery unless for the death of a close relative.

An effort to test whether people named "Cohen" have a common genetic origin has been undertaken, using a genealogical DNA test associated with the Cohen Modal Haplotype (see Y-chromosomal Aaron).

Cohen is one of the four Samaritan last names that exist in the modern day.^{[citation needed]}

Some Jewish immigrants to the United States or the United Kingdom changed their name from Cohen to Cowan (sometimes spelled "Cowen"), as Cowan was a Scottish name.. In Ireland, Coyne is also a similar replacement. The name "Cohen" is also used as a given name.