Alexander Whitelaw Robertson Trocchi (/ˈtrɒki/ TROK-ee; 30 July 1925 – 15 April 1984) was a Scottish novelist.

Trocchi was born in Glasgow to Alfred (formerly Alfredo) Trocchi, a music-hall performer of Italian parentage, and Annie (née Robertson), who ran a boarding house and died of food poisoning when Trocchi was a teenager. He attended Hillhead High School in the city and Cally House School in Gatehouse of Fleet, having been evacuated there during World War II. After working as a seaman on the Murmansk convoys, he studied English Literature and Moral Philosophy at the University of Glasgow, and was awarded second-class honours in 1950.

Without graduating, Trocchi obtained a travelling grant that enabled him to relocate to continental Europe. In the early 1950s he lived in Paris and edited the literary magazine Merlin, which published Henry Miller, Samuel Beckett, Christopher Logue, and Pablo Neruda, amongst others. Although not published in Merlin, American writer Terry Southern, who lived in Paris from 1948 to 1952, became a close friend of both Trocchi and his colleague Richard Seaver, and the three later co-edited the anthology Writers In Revolt (1962). Though Merlin had been established somewhat in rivalry with the Paris Review, George Plimpton also had served on the magazine's editorial board. Trocchi claimed that this journal came to an end when the US State Department cancelled its many subscriptions in protest over an article by Jean-Paul Sartre praising the homoeroticism of Jean Genet.

Maurice Girodias published most of Trocchi's novels through Olympia Press, often written under pen names, such as Frances Lengel and Carmencita de las Lunas. Girodias also published My Life and Loves: Fifth Volume, which purported to be the final volume of the autobiography of Irish-American writer Frank Harris. However, though based on autobiographical material by Harris, the book was heavily edited and rewritten by Trocchi. Girodias subsequently commissioned Trocchi to write erotica along with his friends and Merlin associates Logue, Plimpton and John Stevenson. Under the name Frances Lengel, he churned out numerous pornographic books including the now classic Helen and Desire (1954) and a dirty version of his own book Young Adam (1954). Trocchi and his friends also published Samuel Beckett's War and Memory and Jean Genet's Thief's journal in English for the first time.

Trocchi acquired his lifelong heroin addiction in Paris. He left Paris for the United States and spent time in Taos, New Mexico, before settling in New York City, where he worked on a stone scow on the Hudson River. This time is chronicled in the novel Cain's Book, which at the time became something of a sensation, being an honest study of heroin addiction with descriptions of sex and drug use that got it banned in Britain, where the book was the subject of an obscenity trial. In the United States, however, it received favorable reviews.

Trocchi was then deep in the throes of heroin addiction; he even failed to attend his own launch party for Cain's Book. His wife Lyn prostituted herself on the streets of the Lower East Side. He injected himself on camera during a live television debate on drug abuse, despite being on bail at the time. He had been charged with supplying heroin to a minor, an offence then punishable by death. A jail term seemed certain, but with the help of friends (including Norman Mailer), Trocchi was smuggled over the Canada–US border where he was given refuge in Montreal by poet Irving Layton and met up with Leonard Cohen. His wife Lyn was arrested and son Marc detained, but later joined Trocchi in London.

In the late 1950s he lived in Venice, California, then the centre of the Southern California Beat scene. In October 1955, he became involved with the Lettrist International and then the Situationist International. His text "Invisible Insurrection of a Million Minds" was published in the Scottish journal New Saltire in 1962 and subsequently as "Technique du Coup du Monde" in Internationale Situationniste, number 8. It proposed an international "spontaneous university" as a cultural force and marked the beginning of his movement towards his sigma project, which played a formative part in the UK Underground.

Trocchi appeared at the 1962 Edinburgh Writers Festival where he claimed "sodomy" as a basis for his writing. During the festival, Hugh MacDiarmid denounced him as "cosmopolitan scum". However, while this incident is well known, it is little remarked upon that the two men subsequently engaged in correspondence, and actually became friends. Trocchi then moved to London, where he remained for the rest of his life.