Isidore Isou (French: [izu]; 29 January 1925 – 28 July 2007), born Isidor Goldstein, was a Romanian-born French poet, dramaturge, novelist, film director, economist, and visual artist. He was the founder of Lettrism, an art and literary movement which owed inspiration to Dada and Surrealism.

An important figure in the mid-20th Century avant-garde, he is remembered in the cinema world chiefly for his revolutionary 1951 film Traité de Bave et d'Éternité, while his political writings are seen as foreshadowing the May 1968 movements.

Isidor Goldstein was born in 1925 to a prominent Jewish family in Botoșani. Despite his wealthy upbringing (his father was a successful entrepreneur and serial restaurateur), he left school at age 15, reading extensively at home and doing odd jobs.

In 1944 he began his literary career as an avant-garde art journalist during World War II, shortly after the 23 August coup that saw Romania joining the Allies. With the future social psychologist Serge Moscovici, he founded the magazine Da, which was soon after closed down by the authorities. Soon after he became interested in the Zionist cause and collaborated with A.L. Zissu on the Zionist publication "Mântuirea".

After several attempts to obtain a French visa earlier during the war, he left Romania clandestinely in August 1945, carrying a suitcase full of early manuscripts. He initially traveled to Italy, where fellow experimental poet Giuseppe Ungaretti gave him a letter of introduction and recommendation under the pseudonym "Isidore Isou" to French writer Jean Paulhan, which made his entry into the literary world of the newly liberated Paris much easier.

Intending a total artistic renewal starting from the most basic elements of writing and visual communication, Isidore Isou, assisted by Gabriel Pommerand, organized the first Lettriste manifestation in Paris, on 8 January 1946. During the premiere of dadaist and fellow Romanian Tristan Tzara's play La Fuit at the Theatre du Vieux-Colombier, Isou shouted "Dada is dead! Lettrism has taken its place!"

Through this and other similar stunts – as well as with the help of Jean Paulhan and Raymond Queneau, who placed his work in La Nouvelle Revue in April, 1947 – he came to the attention of Gaston Gallimard, who then accepted his memoire "L'Agrégation d'un Nom et d'un Messie" for publication.

In 1949, Isou published the novel Isou ou la mécanique des femmes (Isou, or the Mechanics of Women), inspired by his obsessions with the 16-year-old muse and later conceptual artist Rhea Sue Sanders. This book was banned by the authorities on 9 May 1950 and Isou was briefly imprisoned and sentenced to prison for eight months (his sentence was suspended); a fine of 2000 francs was imposed along with the destruction of all copies of a book which 1950s' French jurisprudence considered completely obscene. The same year, he also published the first of his works on political theory: Traité d'économie nucléaire: Le soulèvement de la jeunesse (Treatise of Nuclear Economics: Youth Uprising).