One of the novel's most popular ancestors, the medieval romance should not be confused either with modern "romance" (erotic behavior) or Romanticism (a late-Eighteenth and early-Nineteenth-Century literary and philosophical movement in Germany, England, and America). The history of "romance" as a Medieval narrative genre starts with its origins in Medieval Latin romanice, the name for any narrative in the Roman tongue (i.e., Latin). That is, the "romance" named the language in which the work was contained rather than its subject matter. Over time, however, "romance" became inextricably associated with three immensely popular types of narrative or "matter," "the matter of Britain" (Arthurian romance), "the matter of France" (romances of Charlemagne and his "bachelors"), and "the matter of Rome" (romances of Troy, and of classical heroes like Alexander). Historians borrow the terms from Jean Bodel's Chanson de Saisnes (C12), in which the narrator refers confidently to the three "materes" which he expected his audience to identify as a way of positioning his poem about the Saxons. In general, if the characters are knights and ladies, if the plots involve quests and rescues, if the narratives are multi-stranded, and if the outcomes sometimes involve the supernatural, you are reading some form of "romance."
Of the three geographical and chronological "matters," English and French readers are most familiar with "the matter of Britain," tales set in the imaginary era of King Arthur's reign. Searches for a historical "Arthur" identify him as a Celtic warrior that the Welsh Easter Annales of 516 CE identify as fighting with the Britains at Mount Badon and several other battles. He later appears in a Latin text by Nennius where he is called a "dux bellorum" or warlord, who fought "them," an unspecified enemy. "King" Arthur does not appear in all his splendor, together with an array of knight-vassals and a destiny-driven historical arc of narrative, until Geoffrey of Monmouth's Historia Regum Brittaniae (c. 1136), which he claimed to be copying from a manuscript in Old English which he received from Walter Mapes, Archdeacon of Oxford, who (Geoffrey says) discovered it in Brittany. No trace of such an enormous manuscript ever has been found, but if you are reading an Arthurian narrative that treats Arthur as a great king of England who established an empire reaching across Europe to Rome, you are reading a text whose assumptions can be traced back to Geoffrey. (Geoffreys's motives for forging such a document have been endlessly speculated upon, beginning almost immediately with snide comments from William of Malmesbury, another writer of royal British history whose own work led him to suspect Geoffrey of falsehood. For a thorough survey of the surviving chain of evidence, see Siān Echard's "Arthur in History" web page, which supports her survey of English Arthurian literature at The University of British Columbia.
Once Geoffrey's basic framework had gained popular acceptance, French authors used it to develop several important branches of literature addressing their cultural concerns, including the Holy Grail narratives (Quest del Saint Graal, Perceval, etc) and the Lancelot narratives (Prose Lancelot). The "Grail" invention by Medieval (not early Christian, pace Dan Brown) writers radically altered the value system of based on dynastic marriage, secular erotic love and noble families' obsessions with hunting, warfare, and fancy dress. Sacred romance awarded the "pris" or honor of victory to the most pure knight, notably the virgin, Galahad, in preference over his sinful father, Lancelot. German poets spun a Cornwall "franchise" of the Arthurian story-space into the profoundly secular/erotic Tristan and Isode narratives, which had their own line of development until the C12-13 French writers of the "Vulgate Cycle" romances had the brilliant idea to introduce Tristan to Lancelot and Arthur in the Prose Tristan. Shorter Arthurian romances based on individual knights of the Round Table were developed by Chretien de Troyes (Eric et Enide, Ywain, Cligés, Chevalier du Charette), and those knights found their way into the larger compilations of Arthurian narrative. Of those, the greatest single work is Sir Thomas Malory's, the narrative written in 1460-71 and published by William Caxton in 1485 as a single work he titled Le Morte Darthur. (The title's mistaken use of the masculine article, "le," for the feminine noun, "morte," is the result of Malory's shaky grasp of formal French grammar and Caxton's occasional reverence for loyal reproduction of his source manuscript.)
Interpretations of romance often follow the same methods as those used for modern novels, with mixed success. Even the most simple medieval romance usually will yield multiple New Critical interpretations that show the existence of unifying "themes," and artistic uses of irony, paradox or ambiguity which might arguably yield insights about the human condition. New Historicism has challenged many commonplace terms used by New Critics, however. Before the Renaissance, the modern notions of "fiction," the "author," the "work," and even the "reader" had not yet been invented to replace Medieval notions of "historial things" (narratable events generally believed to be true though improvable), "auctors" (ancient texts and persons whose wisdom was presumed to be better than our contemporary knowledge and so worth repeating), "books" (individual manuscript units, perhaps separately manufactured, that might be parts of what we would call larger "works," which themselves might be oral performances lasting many days), and an audience of those who "read" and/or "hear" what the narrator writes/says. The wise student will treat the text like a curious historical artifact of uncertain purpose, capable of being much more than a mere work of art. The Cultural Criticism notion of literature "doing cultural work" often seems helpful--whose agendas and values does the text advance and whose does it impede? Structuralism can develop interesting insights about the text's core structuring concepts. As expected, Feminist and Marxist and Deconstructive analysis also can expose important ideological issues which animate the text.
Click here for some further background on the subject matter of Medieval romance. Hint: it's not about smooching! At least, it's a genre of literature that occasionally leads to smooching but is not primarily about "courtship" in the ModE sense of the word.