Assassination is the willful killing, by a sudden or secret attack, of a person—especially a prominent or important one—typically for political or ideological reasons.

Assassinations may be ordered by both individuals and organizations and carried out by their accomplices. Acts of assassination have been performed since ancient times. A person who carries out an assassination is called an assassin.

Assassin comes from medieval Italian and French Assissini or Assassini, believed to derive from the word hashshashin (Arabic: حشّاشين, romanized: ḥaššāšīn), and shares its etymological roots with hashish (/hæˈʃiːʃ/ ^ⓘ or /ˈhæʃiːʃ/ ^ⓘ; from حشيش ḥašīš). It referred to a group of Nizari Ismailis known as the Order of Assassins who worked against various political targets.

Founded by Hassan-i Sabbah, the Assassins were active in the Near East from the 11th to the 13th centuries. The group killed members of the Abbasid, Seljuk, Fatimid, and Christian Crusader elite for political and religious reasons.

Although it is commonly believed that members of the Order of Assassins were under the influence of hashish during their killings or during their indoctrination, there is debate as to whether these claims have merit, with many Eastern writers and an increasing number of Western academics coming to believe that drug-taking was not the key feature behind the name.

The term "assassinare" (assassin) was used in Medieval Latin from the mid 13th century.

The earliest known use of the verb "to assassinate" in printed English was by Matthew Sutcliffe in A Briefe Replie to a Certaine Odious and Slanderous Libel, Lately Published by a Seditious Jesuite, a pamphlet printed in 1600, five years before it was used in Macbeth by William Shakespeare (1605).

Assassination is one of the oldest tools of power politics. It dates back at least as far as recorded history.