Gilles Jullien (around 1651 or 1653 – September 14, 1703) was a French Baroque composer and organist. He is credited with helping spread the style of French organ music from Paris to Chartres.

Very little is known about Jullien’s life or training. His burial certificate said he was about 50 years old when he died, so he was likely born between 1651 and 1653. It is believed he became the organist of Chartres Cathedral on December 6, 1667. While the date is uncertain, it is certain that he was appointed to this position at a young age. He held this role until his death in Chartres in 1703. After his death, his eldest son, Jean-François Jullien, took over as the cathedral’s organist.

All of Jullien’s surviving music is found in his book Premier Livre d'orgue (Paris, 1690). The book includes about 80 pieces, most influenced by Nicolas Lebègue’s work, organized into eight organ suites based on the eight church modes. According to the book’s introduction, these works were meant for use in religious services, but only one piece—a fugue on Ave maris stella—is directly connected to religious practices. The suites also include several four- and five-voice fugues, showing Jullien’s study of counterpoint. However, like many French composers of his time, he was not very skilled at complex polyphony. His fugues and use of chromatic writing have been described as less advanced. The préludes and récits de dessus are considered his most successful compositions.

Premier Livre d'orgue has several unique features. In the introduction, Jullien claimed to have invented five-voice genres, even though similar pieces appeared earlier in collections by Nicolas Gigault and André Raison, published in the late 1680s. Additionally, the book ends unusually with a choral piece titled Cantantibus organis. Another vocal work by Jullien, La Crèche de Bethléem, is only known by name. A second organ book was planned but was never completed.