Epic is a narrative genre characterised by its length, scope, and subject matter. The defining characteristics of the genre are mostly derived from its roots in ancient poetry (epic poems such as Homer's Iliad and Odyssey). An epic is not limited to the traditional medium of oral poetry, but has expanded to include modern mediums including film, theater, television shows, novels, and video games.

The use of epic as a genre, specifically for epic poetry, dates back millennia, all the way to the Epic of Gilgamesh, widely agreed to be the first epic. But critique and discourse has continuously arisen over this long period of time, with attempts to clarify what the core characteristics of the “epic” genre really are beginning only in the past two centuries as new mediums of storytelling emerged with developing technologies. Most significantly, the advent of the novel, such as classics like Tolstoy's War and Peace which began to be referred to as “epic novels”, caused critics to reconsider what can be called an “epic”. With this discussion, epic became a larger overarching genre under which many subgenres, such as epic poetry, epic novels, and epic films could fall under. However, the nebulous definitions assigned to even the long-standing ancient epics due to their ubiquitous presence across vastly differing cultures and traditions, are still a topic of discourse for today's literary academics, and have caused lingering difficulties in creating a definitive definition for the umbrella term of “epic” as a genre.

Epic originally comes from the Latin word epicus, which itself comes from the Ancient Greek adjective ἐπικός (epikos) deriving from ἔπος (epos), meaning "word, story, poem."

The word Epic, throughout the years, has adapted to different meanings that stem far away from its origins. In Ancient Greece, Epic was used in the form of a noun. Epic (noun) refers to a long poem, book, movie, etc. that tells the story of a hero's adventures. The earliest epics were long poems performed out loud that told these grandiose stories about heroes. Today, in modern society, the word epic has been expanded and associated with all kinds of long literatures that still underlyingly focus on the values of a given society. It is often used as an adjective. Epic (adjective) refers to something very great or large and usually difficult or impressive. In addition, the word epic can be used to describe any media that has a large scope, that speaks about the human condition and that is ambitious with artistic goals. Star Wars, for example, is considered a modern cinematic epic.

Providing a plethora of narrative tropes, the Mesopotamian Epic of Gilgamesh, as the first recorded epic poem, would lay the foundation for the entire Western branch of the genre. Both the Old Testament and New Testament borrow many themes from Gilgamesh, which in turn has been found to draw from older Sumerian tradition. As such, some anthropologists identify Jesus as an embodiment of the same mythical archetype. Some similarities, among others, include stories of:

Just as it provided a blueprint for biblical traditions, many other pre-Christian mythos and religious epics have also shown to be influenced by Gilgamesh, including those of Buddha in Buddhist tradition; Krishna in Hindu tradition; Odysseus, Perseus, and Dionysus in Greek tradition; Ra, Horus, Osiris, and Amenhotep III in Ancient Egyptian tradition; Romulus in Roman tradition; and Zoroaster/Zarathustra and Mithra in Zoroastrian tradition.

The Bible similarly extended its influence into existing epic literature such as the legend of King Arthur, which, as it exists in the modern day, has been interpreted to be loosely modeled upon the life of Jesus, however this was not always the case. Arthurian literature had originally been based on pre-Christian, Celtic folklore and may have been based on a British warrior (5th–6th century) who staved off invading Saxons. During the early christianization of the United Kingdom, the Church tolerated new converts observing their older, pagan traditions. However, as the British Church grew in power, events taking place in Europe (such as The Crusades) inspired authors to reshape the traditional legends with Christian undertones. Author Robert de Boron, for instance, translated the legend into French in 1155, in which he would conceive of the now-iconic addition of the sword-in-the-stone legend, and would expand upon the Round Table lore whereby Arthur had twelve knights just as Jesus has twelve disciples.

Specific echelons of popular culture draw from a variety of epic narrative tropes. This may preclude to genres such as heroic fantasy, sword and sorcery, space opera, fantasy adventures, and high fantasy. Some even draw influence from each other, just as ancient sources. For example Frank Herbert's Dune Saga inspired the Star Wars trilogy and the Alejandro Jodorowsky's Jodoverse.