The hashishim were a Ismaelite (a subsect of Shi'ite Muslim) order, operating in the 11th and 12th centuries AD and based in the mountain fortress of Alamut in northwest Persia (now Iran). By modern standards, the order would certainly be called terrorist, and in fact may have been the first to employ terrorist warfare as we know it; its members were trained as suicide troops, and targeted prominent individuals in an attempt to further the group's political aims. The English word "assassin" was probably first used to describe this order and later generalized to mean any politically motivated murderer. The etymology of the term is somewhat imprecise, but it is most likely a corruption of "hassashin" ("follower of Hassan"), rather than one of "hashish".

The order is commonly thought to have used drugs to indoctrinate its members; one comparatively well-known story (originating with Marco Polo) mentions hashishim initiates drinking hashish in liquid form and subsequently experiencing visions of Paradise. However, this story is contradicted by most of the other sources relating to the order (not to mention the fact that it was written several decades after the events in question), and thus should be taken with a grain of salt. Religious brainwashing techniques of some sort are fairly likely, but as the order's records were destroyed with Alamut, little reliable information is available on the subject.

The order was founded by one Hassan i-Sabah (alternate spellings:Hasan-e Sabbah, Hasan I Sabbah). He is known to have been a well-educated individual, and to have traveled extensively, but much of the surviving knowledge relating to him was passed down through his political enemies and is therefore probably not to be trusted.

The order is thought to have practiced initiation rites similar in structure to those of Freemasonry, and are known to have had strict principles of obedience and secrecy. Perhaps because of this, they play a role in many conspiracy theories involving other secret societies of the time (particularly the Knights Templar). Numerous stories and anecdotes relate to this, but few are very credible.

See also: assassin, Hasan-e Sabbah.