The Holy Grail (French: Saint Graal, Breton: Graal Santel, Welsh: Greal Sanctaidd, Cornish: Gral) is a treasure that serves as an important motif in Arthurian literature. Various traditions describe the Holy Grail as a cup, dish, or stone with miraculous healing powers, sometimes providing eternal youth or sustenance in infinite abundance, often guarded in the custody of the Fisher King and located in the hidden Grail castle. By analogy, any elusive object or goal of great significance may be perceived as a "holy grail" by those seeking such.

A "grail" (Old French: graal or greal), wondrous but not unequivocally holy, first appears in Perceval, the Story of the Grail, an unfinished chivalric romance written by Chrétien de Troyes around 1190. Chrétien's story inspired many continuations, translators and interpreters in the later-12th and early-13th centuries, including Wolfram von Eschenbach, who perceived the Grail as a stone. The Christian, Celtic or possibly other origins of the Arthurian grail trope are uncertain and have been debated amongst literary scholars and historians.

In the late 12th century, Robert de Boron in Joseph d'Arimathie portrayed the Grail as Jesus's vessel from the Last Supper, which Joseph of Arimathea used to catch Christ's blood at the crucifixion. Thereafter, the Holy Grail became interwoven with the legend of the Holy Chalice, the Last Supper cup, an idea continued in works such as the Lancelot-Grail cycle and consequently the 15th-century Le Morte d'Arthur. In this form, it is now a popular theme in modern culture and has become the subject of pseudohistorical writings and of conspiracy theories.